Are you referring to the Tab on the Project site itself? I don't think you can change that, but you can change the "Issue Type" names. For instance, if you wanted people to submit "questions", you can go to Setup>Project Preferences>Statuses, then click on the "Issues" Tab, and then click on one of the Issue Types. You'll see at the top there is the name of the Issue Type. You can change that to whatever you like (i.e., "Questions" in this case).