Is there anyway to change the main ringtone? There are some options built in but can I use another one I have downloaded?
This is a tricky one. However, I have the solution for you.
You need to create folders on your Internal SD card to make this work.
1) Open your "My Files" app (I think you need to use this app).
2) Open /sdcard/media (create it if it does not exist by press menu key->Create Folder)
3) Once in /sdcard/media/ create folder "audio"
4) Open audio and create 3 more folders: "alerts", "notifications", "ringtones"
5) copy your ringtones to the folder ringtontes (/sdcard/media/audio/ringtones)
By placing the files in the ringtones folder you will have access to them for selecting them in your ringtone menu from settings->Sound and Display->Voice Call Ringtone and these files will not show up in your media player (so you don't have to see your ringtones while playing music).
Note: this also works for the notifications folder and the alerts folder by placing files in the correct folder.