With SimpleTix, you can customize your site fully, even to the extent of changing  your labels.  To change the labels :

  1. From the admin panel, folder: /AdminPanel/ 
  2. Go to the settings tab, it's the one on the far right side. 
  3. Click settings, in the sub-menu choose "Other Settings" 

  4. On the bottom of the page, click "Edit Labels"

From here you can search for different labels on your site and overwrite them. 
We recommend making one change as a time, saving, then in another browser preview the change on your site.