How to access objects created by a different user User A created few objects with schema "UserAPriv", but now he is either leaving the company or changing the department.
Now we need to restrict his access to his previously created objects and make some arrangements so that other team mates from previous project can access his objects and work normally
Now we need to restrict his access to his previously created objects
  and make some arrangements so that other team mates from previous
  project can access his objects and work normally


It may be the case that your user was db_owner, in this case all the objects he created are already owned by dbo, in this case you should do nothing at all and simply drop the user:

drop user A;


There may be a situation when the user owns some schema and in this case database engine will prevent you from dropping user:


  The database principal owns a schema in the database, and cannot be
  dropped.


To be able to drop a user-owner of a schema you should first change the ownership of a schema:

alter authorization on schema::UserAPriv to dbo


Now you can try to drop the user and he will have no access to your database at all.

If the principal was also a grantor of permissions, database engine will prevent you from dropping user again:


  The database principal has granted or denied permissions to objects in
  the database and cannot be dropped.


in this case you should first find all the permissions where he is a grantor:

    select user_name(grantee_principal_id) as user_,
           object_name(major_id), 
           permission_name, 
           state_desc
    from sys.database_permissions
    where grantor_principal_id = user_id('A');


Then grant all these permissions as dbo, and then revoke them as User A:

grant select on UserAPriv.t1 to SomeUser as dbo;
revoke select on UserAPriv.t1 to SomeUser as A;


At this point you can drop User A.