And they get much larger but this page is for Home owners.
So I will not bother with the larger tanks. 
Replacing An expansion tank can be very easy in most cases, but you are dealing with
VERY hot water and you can get scalded.
It may be best to have a heating contractor do it.
but like the one I did on the Weil McLain boiler,
turned out to be a real pain.

This is also a #30 tank And this would also be easy to replace.
Ok So now we have determined if we should replace it or not and what type of tank we need. So lets replace the thing already.