membrane housing cap stuck?

This seems kind of stupid to make a thread about, but I was going to try to change my ro membrane out but the housing cap is stuck. I dont remember ever tightening it so much so I dont understand how it could be this tight. Are there any safe ways to loosen the cap? The housing has an old membrane in it that I dont really care about

^Thanks but actually no wrench came with the system to untighten the membrane housing, just the canister filters....anyhow, got it off with some vise grips, was especially careful not to replace the cap too tight this time.

May as well ask now though, do i need to let the system run for a while since i just replaced the membrane and filters?