Keep in mind that "editing the name and password" of the existing account does NOT result in that same account with a new name. You only find that out when you restart, and the system creates a NEW account with the same name as the old one (before you "edited" it!),
And, there's nothing in that account, beyond what the system does in creating a default account.
Here's the quickest way BACK to your first account.
Edit the name of your current user folder (change the name to something unrelated). You'll probably notice that your current user is AGAIN named admin, and not the name that YOU changed.
Change the user account folder to the OLD name (admin, I think you said), and restart your Mac. You SHOULD then be back in your original account, with your old files and apps.
One possible problem, is that IIRC, the account name "Admin", is one that OS X considers a "special" or protected name. The system might not let you change the user folder to that name. It's a shame that your "friend" used THAT name for the first user.
Anyway, now you know that OS X will fight you every step of the way, unless you know the "rules" about the user accounts.
Best way to rename a user account, is to create a new user account (in System Preferences/Users & Groups pane) Log out, then log back in to that new user. Copy all your files to the new account. Delete the old account (only through the Users & Groups pane). I don't think you can delete an account named "admin" (remember the "protected" name?), unless you are logged in to the "root" user - which is a whole other subject. Or, you can choose to ignore the "admin" account, using it when you need a little help if needed for troubleshooting your system. Good to keep one account that you don't often use.