At the time of writing, latest release was freshtomato-E2500v3USB-NVRAM32K_RT-N5x-MIPSR2-2021.8-Mega-VPN
Zip file should be unpacked before uploading.
Open 192.168.1.1 and go to the firmware update page. Default username and password are admin and admin.
Select the .bin file, and wait completion.
Router should be restarted.
It can take some time for router to boot, no need to panic, just wait 5 minutes to be on the safe side.
Default username and password are root and admin, respectively.