How do I edit the list of account types?

I am new to SuiteCRM, and not yet familiar with the general ideas in the user interface.
I need to add a few new entries to the list of choices for the Type field in Accounts. I assume there is a way to do this without opening up the PHP source code, but I can’t figure it out.

Is there a general User Guide document where one can look for this kind of simple stuff?

Goto Admin, Drop Down Editor should be the first item in the list account_type_dom