Stop Bitcoin, as in close the program.
Press the windows button and on the search field of the start menu write
explorer %APPDATA%\Bitcoin
and press Enter
On the dir that opens, copy the file called wallet.dat to another location
Delete everything safely if you wish, or in alternative delete everything except the wallet.dat file.
Reinstall Bitcoin
On a side note: I don't think uninstalling Bitcoin will delete any files inside the data dir. Not even sure if the uninstallation procedure asks if the user wishes to delete the data dir.
You'll have to delete them yourself.