You can't delete them probably because they're in use, kill them from task manager or reboot your pc
If you can't update, re-download the game from the website and replace the old files (backup the folders "stamps" and "saves" if you want to keep them, and "powder.def" if you want to remember your password)

alt control delete

Not directly, it allows you to do that: go to Processes and kill all powder.exe or similar