You will need the Full Write Groups permission to edit a group.
Sometimes, groups need to be capped or limited to a certain number of people. This can be done easily within the One Church Software.
Open the Group
Click Groups in the left-hand menu to open the listing. Find the group you want to edit and either click the group name or click the 3-dots menu at the start of the row and choose View.
Set the Capacity
From the group's detail page, click the Actions button in the upper-right and select Edit group. In the pop-up, go to the Options tab and enter a number in the Max Capacity field. This is the maximum number of current members allowed in the group. Click Save.
How Capacity Is Enforced
Once a group reaches its maximum capacity, no additional members can be added, regardless of how they're being added, whether manually, through a group sign-up, a registration form, or a bulk/mass add. The limit is checked at the moment a new member would be added, so it stays accurate even as members join or leave.
Removing the Limit
To allow unlimited members again, open the group, click Actions > Edit group, go to the Options tab, clear the Max Capacity field, and click Save.