It can be changed from the bottom. Put a clamp on the incoming fuel line to pinch off the flow; I use small vice-grips. Remove hose from filter, use a deep socket to remove the filter. Use the new filter to select the socket size.
Use a bit of fuel proof teflon tape (yellow), or pipe dope, coat the threads on the new filter, thread it in and tighten with the wrench/socket. Install the hose, tighten clamp, remove vice-grips.
Prime the generator (push/hold OFF rocker, pump starts after a few seconds) until the pump quiets down, then start. Check for leaks.
I didn't use tape the first time I replaced the filter, had a leak...