I can't really change my pen buttons on Ubuntu so I was wondering if there was a way to change the defaults for the right and left click in Krita. Tried changing the shortcut keys but I don't see their options. Where can I find them?

btw I can't seem to change my theme to dark. I go to configure Krita but none of the tabs seem to have the theme change.

Changing the theme will be in Krita 2.5, it isn't in 2.4 yet. If you have a 2.5 alpha or beta, you can find the option in the Settings menu, not the configuration dialog. Swapping left and right click is possible in KDE with the systemsettings utility, I'm not sure whether Ubuntu has something similar -- I'm traveling and haven't got my ubuntu vm on this laptop.