The stpes provided by hatstead above should very well in PSE 11. May you are not following the steps correctly or you are not able to make a precise selection. You have to use selection tools very carefully and precisely select the section of the photo that you want white. Then use either
- Go to Edit menu>fill selection>contents - use white.
- Select Brush Tool (Shortcut B) . Set foreground color to white . Paint over the selected sections of the photo that you want white.
See this adobe help link for making selections