Removing Lenses in Dacor Vista-Vu Dive Mask

I have an old Dacor Vista-Vu dive mask with corrective lenses that I us for snorkeling.

The last time I used the mask I was getting water in. Looking at the mask it appears that sand has worked its way between the lenses and the mask. I would like to remove them and clean the sand out but I am not sure how to do this.

When I originally purchased the mask the lenses were separate and installed by the shop so it would seem there should be a way to do this. The shop is no longer there so I can not ask them.

Any help would be appreciated.

Thanks