make a backup of the "saves" folder under .minecraft
you can find .minecraft by searching %appdata%. This might reset your settings, but you will still have your worlds. I think it's a good idea to delete the .minecraft folder when you have uninstalled it, to be absolutely sure everything is reset. Then just paste the "saves" folder back in. Don't do this if you use a custom save location.
Although you might wan't to try changing your save location first. Make a new "Installation", then press it, and change the "game directory" to another folder (make one). Everything will be reset, but you will still be able to go back to the old one by switching "intallation".
Oh and make sure you have updated your launcher
