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No, user.php isn't supposed to be edited, definately not for design changes. No, go to the system admin -> templates to open the Template Manager, that's where you can edit all the templates to change the look and feel of your website. If you only have the default template set, you're going to have to clone it first, because you can't edit the default templates (because that is there to change back to if something goes wrong). In your cloned set, go to the system templates, and edit the system_userinfo.html template (not the file, but use the template manager!). That's where you can change the look of the user profile page.
Herko