I assume you created your slideshow in the Elements Organizer. If so, once you output it as WMV, it can't be edited. (Unless you also saved a copy of the work file, a .pse file.)
If you're sending your finished slideshow to Premiere Elements, it's best not to output a WMV but, rather, to select the option to Send to Premiere Elements. This will send the slideshow to the Premiere Elements timeline and, if you want to edit it in Premiere Elements, you need only right-click on the file on your timeline and select the option to Break Apart Slideshow.
When you create an Elements Organizer Slidesho, you are given the option to save your work to the Organizer as a project (.psess file) as well as to the .wmv file if that was your Output choice. Did you save the work as a project (.psess file)? If so, then re-open that and edit your text.
If you create a slideshow in the Elements Organizer and output it as a wmv video with the appropriate sizing, that wmv can no longer be edited in the Elements Organizer. You can save it to the Elements Organizer, but not edit it there. It can still be imported in Premiere Elements with its Get Media (versions earlier than 11) or Add Media (version 11) and edited in limited ways unless you break it apart with trimming and such.
As SG suggests, the preferred way is to create the slideshow in Elements Organizer and then use the Output command of Edit With Premiere Elements Editor. That will take your slideshow as a .psess file into Premiere Elements where you can use the Break Apart Elements Organizer Slideshow command, allowing the opportunity for further significant edits.
If you do not have Premiere Elements and are creating the slideshow in the Elements Organizer of Photoshop Elements, the Output to .wmv can be a perk since you can take the .wmv into a program other than Premiere Elements in order to create the DVD-VIDEO on DVD disc if that is your goal. A lot depends on what you want to do with the slideshow once it outputs from Elements Organizer and how much more editing you want to get done after the output.
Welcome to the forum.
Steve G. and ATR have explained the methods of both creating a SlideShow, and getting it into Premiere Elements.
With that WMV output file, your choices for additional editing will be limited, but if I read what you wanted to do correctly, there may be a workaround.
You mention changing some of your text. Let's take a look at this process.
Is your text (Title) appearing by itself, or is it ontop of a Slide (Still Image)?
If it is a separate Title, and not over a Still Image, then in PrE, just create a Title, with your desired Text, and place it on a Video Track that is higher than you WMV Clip. Adjust its Duration to be a bit longer, than the Title in the WMV and any Transitions in it, then apply a Cross-Dissolve on either end of that Title.
If the Title in the WMV is over a Still Image, i.e. superimposed into that Still Image, you will do the same thing, but with one more step. Import the Still Image, which matches the Still Image at that point in your WMV, and place that on a Video Track above the WMV, say Video Track 2. Adjust its Duration to be slightly longer than that same Still Image in the WMV, plus any Transitions that it has. Now, create a Title with the correct Text, and place it on a Video Track above the WMV and that Still Image (the one that matches the Still in the WMV, say Video 3. Adjust its Duration to match that Still Image on Video Track 2. Add a Cross-Dissolve to the ends of both that new Still Image, and the New Title.
The weakness of these methods is that to get Transitions to either/both the New Title and the new Still Image, you will need to "cover up" anything happening on the WMV, so the timing will be a bit different.
Still, the ultimate method is the one suggested by both Steve G. and ATR - Send to Premiere Elements, and then Break Apart. The methods outlined above are ONLY if all you have from your Organizer SlideShow is that WMV. They are stop-gap methods, but will work just fine, with the exception of that slightly altered timing.
This shows how one would "replace" a Text Title, that has been burned into a WMV.
In this example, the WMV with Transitions and a Text Title burned in, is on the Timeline. The CTI (Current Time Indicator has been placed over the middle Slide, showing the burned in Text. As the Transitions are also burned in, they do not show, as they are now part of the WMV.
This example shows that I used Beat Markers, to go just beyond where the Transitions, and the second Slide with the burned in Text are. I added about 3 sec. on each end, so that when I add my "clear" version of the second Slide, and the new Text Title, and then add Cross-Dissolves to those, I will not see the Transitions, or burned in Text from the WMV. This is that "loss in timing," that I mentioned.
Hope that this helps. Because of that loss in timing, it is not a perfect solution.
As stated above, if possible, the Send to Premiere Elements and Break Apart ARE the perfect solution.