I can see your problem! Have you contacted support about this? They may be able to show you a way to modify the A record, or do it for you (though I understand that might not be acceptable, as you may need/want the ability to change it yourself).
To transfer the domain to another registrar, just initiate the transfer from the new or receiving registrar’s site (assuming, or course, you have checked that the new registrar has a way for you to get at the A record!).