How do you upload a custom emblem? I don't want to use any of gtalogo.com's logos because I don't like them. Thanks. I would like to use
for my crew https://socialclub.rockstargames.com/crew/seville_piru

This exactly, you cannot do it anymore unfortunately.I believe the ability to upload custom crew logos has been patched / removed way back around update 1.13. They removed this feature because people were putting nudity and explicit content as their logos.