These AEGs have a ~dovetail on the magazine that slides into a slot on the front of the trigger guard if I remember right - is this the area that seems to be to tight on your new mag?
Generally I recommend modifying the part that's cheaper / easier to replace when there's fitment issues in case the modification fails, so ideally we'd modify the magazine here rather than the receiver. That said, if the slot in the receiver is to narrow it might actually be better to widen it slightly than to have to modify every single mag you get... So, study the issue and approach it thoughtfully.
Take a sharpie and put a layer of ink on the surface of the rail that goes into the slot and wait until it's dry to the touch. Insert and remove the mag a few times and look at the area where the marker has been rubbed off - this will tell you where it's tight IE where you want to remove material. Pick up a set of small files (or some sand-paper) and remove a very small amount of material in the area that's rubbing, then repeat the above and see if it's still to tight - if it isn't, yay; if it is, look at where the marker rubbed off and repeat. Only take a little material off each time - speaking from experience, better to spend 15min getting it perfect than to have to wait 5 days for a whole new mag