changing from 220v to 120v

There are a pair of Bryston monoblocks I am interested in that are 220v. The dealer says he can change them to 120v before shipping. I know next to nothing about electricity. Is the conversion easy to do correctly and well? Or migth there be non-trivial issues involved?

thanks for your thoughts.
Bryston probably knows.
+builder3, call Bryston.  While your at it, make sure with Bryston that there are no warranty issues if you do it yourself.
James Tanner, owner of Bryston, recommended not buying amps built for a different country. I am going to heed his advice.  I'm also worried the warranty might not transfer.

thanks for all the responses. 
I woulds never buy a 220v amp to be converted get 110v only it could be a problem.