PRE10 nd PRE11 can run side by side on your computer so there is no need to uninstall PRE10, during beta testing we did import projects from pre10 into PRE11 and issues were encountered by some testers but with both versions on your computer, not so much of an issue, if it does not import correctly, then finish the project in PRE10
I agree with Robert. It is always best to finish a Project, in the version, in which it was started. That eliminates the potential for issues developing, when a Project is migrated from one version up to another. With most Adobe programs, differernt versions can co-exist, as the programs do not overwrite any previous versions - they install into a different folder structure.
The only thing that you might keep in mind, is that when you install PrE 11, file associations, that are common to both programs, say the PREL's, will be directed to PrE 11. All that means is that to Open your Project in PrE 10, just launch PrE 10, and choose Open, navigating to that Project, if you do not see it in the list of "Recently Opened Projects." If you were to Dbl-click on that Project in Windows Explorer (or Finder on a Mac), it will want to Open in PrE 11. Just launch the desired program first, and use it's Open dialog to get to your PREL.
I always leave my older Adobe program version installed, until I learn all of the changes in a new version. There are always some changes, and depending on the program, and the version, it can take a bit, to get comfortable with all the changes - some operations change names, or perhaps their locations. A perfect example of this is the Export Menu in PrE 4. Almost everything there was moved to the Share Tab in PrE 7. That hung up a lot of people (and still does), for a while.
When you have completed your PrE 10 Project, and output the final file, you might want to do a Save_As, changing the Project's Name slightly, and then Open that Save_As version in PrE 11, to see exactly how it translates in the new version. You can also use that Project to test and experiment with PrE 11, to see where things have changed, and what has been added.