The easiest thing to do is change your ID to the one called My ID. This ID pack is pre-installed on the phone and is very basic and has no installed widgets or applications. From there you are free to install any themes, etc. from the app store that you want.
You will still have the "ID" button next to the menu key, but other than that you will be pretty basic Android build.
You can also delete any ID packs you have downloaded by pressing the ID button then Menu > Manage > ID Pack you want to remove > Remove.
Thank you to for the quick reply from MPerina1 and garrettz1. I downloaded the clean at activation and think I am going to stick with that. I wanted to use a theme but it is too much trouble and I could end up with it not working properly.
Check out a fun infographic that teaches you how to increase storage, enhance security, improve battery life and clean your device.