You can set your own domain by either parking it or adding it as an add-on.
To make it the primary address ( and remove your sub-domain ) ... make sure the nameservers are pointed to x10 ( ns1.x10hosting.com and ns2.x10hosting.com ) then posting a message in the Upgrade / Downgrade / Changes section requesting the change.
I believe ( but could be wrong - I don't use FTP ) but if you click on FTP accounts, it gives you some instructions on how to access your account via FTP. ( like mine says : You can login to a FTP by entering projectmicah.com as your FTP host and the username and password of the account you wish to log into. )