I guess you are referring to the Site Templates
for .LRN 2.2.0.
If so,
go to htpp://yourdomain/dotlrn/admin
then lick in the Site Templates link;
after that, click on the "Admin Parameters for Site Templating". And there you can change
the default Site Template for user and communities.
Note: this only effects people that have not logged in yet.
We should probably add a "reset portal template for all users" button (with a caution notice, b/c it punishes the few that have customized their layouts).