Safari, like every other application on the Mac, has a Preferences window. To open the preferences window, pull down the Safari menu, and select the Preferences... option.
(In general, checking the Preferences window is a good thing to do when you need help figuring out how to change something an application on the Mac.)
In the preferences window, there is a pane labeled "AutoFill." If you click on this option, you will see three different sources for AutoFill information. Next to each source you will see a checkbox which will turn it off, and an Edit... button which allows you to remove individual AutoFill entries.
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DON'T rename your home folder - it causes all kinds of hassle as you loose all your settings including playlists for iTunes, bookmarks etc etc.
But if you are determined to do it.
If you want to 'rename' the home folder the best way as you may have discovered is to create a new account (System Preferences > Accounts) and in the short name description, call it what you want your home folder to be called.
Then copy out the documents from the account you are transferring from into the new home folder, and then delete via Account Preferences the old account you have just transferred from.
As to why Apple allows you to easily rename the home folder is beyond me too, but maybe something will be done in time.
