From standard to beginner

[Merryl]

Theyre just locked if he has more than one character per server. I think you can designate which is a main character via the lodestone. I've never tried it personally since I've always had my account set to entry.
The only other way is to delete or move the other characters from that server.
Your friend may have to pay for standard one more time though to be able to use the character delete function.