How do I remove someone from a group text

If any member of a group text is Android, you can't remove anyone. The only groups you can modify would be if everyone is an iPhone user on iMessage. This is not an Apple issue. This is a carrier limitation of SMS.

While you can only remove someone (or yourself) if ALL users are on iPhones, you can "mute" their texts so they are less annoying. See this article for instructions:

https://www.lifewire.com/leave-a-group-text-4149831#