Paterson proofer question

Sorry for the silly question, but I recently found a second-hand 8x10 Paterson proofer with 120 and 35mm glass and I can't find a manual online. I would like to swap the 120 glass (currently installed) for the 35mm. I assume I need do something with the 'little black hinges' but am worried if I use force I'll break it. I am missing something really obvious here... perhaps the glass can't be exchanged at all? Any help appreciated. Thanks.

I never knew that both pieces of glass were available with one 'backboard' for want of a better term. I have a Paterson 120 version and have never had an inkling to try to take it apart.

I have an all purpose 8x10 proofer for 35mm- 4x5 thatonce was a 35mm proofer (not Paterson). The galss came out of its from it being left vertical in a hot place for many years in storage.

I replaced the now broken glass with integral carrier for a blank sheet, and now proof most often after the negs are sleeved into the whole page negative storing solutions from PrintFile and the like.

If you pry out the little black plastic caps the fixing screws are visible. Back in the day,the glass part was available as a separate item from Paterson.

Thanks for the replies. I will try and be a little more forceful with the black plastic caps then ;-) Thanks.