Linux user quotas can be edited with the commands edquota or setquota on the shell. While edquota opens the quota settings in an editor like vim, setquota allows you to specify the quota settings on the command line.
Example for disabling the quota for the user "testuser":
setquota -u testuser 0 0 0 0 -a
Example for disabling quota for the group "testgroup":
setquota -g testgroup 0 0 0 0 -a