Just so we are on the same page,
Angelfish are egglayers so they will never be pregnant. Only the livebearing fishes such as Guppies, Mollies, Swords, and Platies for example can be pregnant.
Angelfish can be "gravid" which means that they are holding eggs.
If you have no intention on breeding these fish, you need to do nothing. A female Angelfish can carry eggs her entire adult life and never spawn.
What you do have to watch out for is if this rounded appearance is from bloat. If your fish is eating and pooping on a regular basis, it does not have bloat.
Hope this helps...