WordPress.com-registered domains

Question

I got the client who paid for WordPress hosting with wordpress.com. They also purchase domain with wordpress.com but we did completely new WordPress installation on another server and would like to now re-point that domain to another IP address is that possible? I have a option inside that WordPress installation to Edit DNS Record but when i try to put my IP address like they suggest: A 1.2.3.4 its coming up with an error: We can't save these records because they don't look right to us. Check the errors below. Please contact support if you are unable to resolve the problem.

Can any one help or advice.

Many thanks,