How to replace /access CMOS battery in Mini PC PN61?

[POSPD]

The CMOS battery needs replacing in Mini PC PN61. Have taken the bottom off but looks like the CMOS battary is located on the other side of the motherboard not instantly accesible. How do you release the motherboard from the metal frame to access the battery? Are there any instructions / videos that show where the motherboard fixings are as nothing is readily visible. Any guidance would be apprecaited. Thanks....