You should try to make this sort of change in a PHP-based 'advanced' theme (or in the future in a theme layer), instead of changing the core code:
This way, your changes will survive any upgrades you make to the Q2A application itself.
The function you are most likely going to need to override, or at least the starting point for investigating, is nav_user_search().
However, that link is important for your logged-in users to keep track of their scores and the questions they have asked or responded to, so you will want to preserve this link somewhere your users can access it.
It may be that you can achieve some of what you need by instead writing a plugin to add functionality to that page using the 1.4 widget facility (which you can try out right now in the developer preview). This is the approach I have taken with my own changes to that page.