How do I create a new character with the Mac OSX? I'm hunting for the information I need to change, or erase. I think its in my library somewhere, but I can't find it.

which Ultima game? If it's Savage Empire and Martian Dreams the only way to start a new character is to either re-install or run the setup program if the MAC version has it, if it's Ultima 2 sadly you have to uninstall and reinstall since the game was originally made to use disks.

It is Martian Dreams for the Mac.

There should be an option somewhere in the menu bar to reset all information. Whatever you do, don't change the actual app, the changes are all in the Library.

Actually, I found the hidden library on the Mac, and I can make my changes there. Just do shift+command+G and type ~Library, and you can see your hidden library. It took me a while, but it's in the GoG folder, under the preferences folder.