Just to let you know, you can only do these things if you are an account administrator or above.
Within any "team" you have created in your account there is a search box as you can see in the below image.
Here you can search for a specific user. You may want to delete the user from the team, you might even want to change the access level for the user making them a contributor or listener. Click here to see the difference between a contributor or listener is.
If the account has multiple pages of users within a team, the search bar will help the account administrator find users easier.
There is also a search box available when you are looking to add users within a team.
This will bring up every user created within the account. In some cases, this might be quite a few users. By typing in the user, you will filter all users to the specific one you want.