How do you rollback firmware to earlier version please

Volumio Information

I have the latest firmware version 2.861, but it is very flaky as it loses connection from PC to RPI3 where it is installed so that the PC interface has no connection clicking on settings as well comes up blank that is no drop downs. My music is stored a synolgy NAS and has connected and worked for months without any issues on both volumio setups but now it wont play any music from the NAS. I have to reboot the system several times to attain some stability. so i would like to roll it back to the previous version which worked. so can someone tell me how to do that easily thanks.
Volumio Version: