1. First select the group you want to leave.
2. Tap the group’s avatar in the top right corner or you swipe left from the right side of the screen.
3. Now tap on Settings, scroll to the bottom of the page and
then tap or click Leave Group.
You can also see 'End Group it means that you're the owner of that group so that is you created that group, If you select End Group you will delete the group entirely.
To leave the group without deleting it, you can change the group’s creator.
For iPhone (iOS)
The steps are basically the same with Android, here is a recap though.
Select the group you want to leave.
Tap the group’s avatar in the top right corner or swipe left from the right side of the screen.
Tap setting, come down to the bottom of the page and then tap leave group.
If the above seem too cumbersome or doesn't work for your device platform. Do this simply one instead.
Text #STOP to any group number.
forbid communication from new groups in the future.