how do I change change themes?*

This discussion is related to the Minalla Yellow addon.

found a newer theme i like, how do I change it

sahotataran

Depends - if you just want to change the colors then you can just do it through CSS. otherwise if you want to change the whole layout then you will have to change it in the
Theme -> Views -> default.master.php
if there is none then you will have to create your own default.master.php.