I have some experience working with similar things, but no actual knowledge of dive masks.
Just thinking out loud, so to speak, I would assume that the lenses go into channels around their edges. If they’re not glued in, carefully working the channel lips off of the glass with a suitable little pry tool ought to work. Said tool should have a blade that won’t cut the mask - rounded edges, maybe even made of plastic. Look closely to see if they should come out from the front or the back of the mask. If the lenses are glued in, it could be tougher, but I’m guessing that probably the glue can be removed without solvent.
For installation of the replacement lenses, a lubricant could be very helpful. My first thought is silicon spray or grease. If glue is used, the unset glue would probably act as a lubricant.
ETA: Soaking the mask in hot water to enhance its pliability is probably helpful or even necessary.