All releases for the different equipment is under Announcements from the main forum screen.
This is the one for my Fire TV 4k Stick
EDIT: this is not the one I am beta testing, I had issues with 7.29.2
Not sure why the 7.30 betas are not listed anymore…**
as for side loading that depends on the equipment that you have, you can google it for your device.
The way I do it is using a windows laptop, it has to be on the same local LAN.
