You can rinse the glass square in soapy water if it is too dirty. Then clean again with lens cleaning liquid and microfiber cloth to remove any maps and fingerprints.

Depending on how dirty the lenses are you might need to disassemble it. Make sure the top lens is clean. Unscrew the retaining ring.

If the top lens wont come off on its own you'll need to use some force. I found that using the suction cup from ifixit kit works great. Be really careful! I pulled very hard and the top lens jumped , crashed on the metal assembly and then landed in my lap. The lens was by miracle without any scratches or missing bits.

Clean both lenses with lens cleaning liquid and microfiber cloth.

Reassemble lens assembly.

Reassemble the whole enlarger body back together.