Hi Carrie,
We have designed our theme this way. The secondary link is for the external url. To open it on the same window it needs a bit of code customization. you have to remove "_blank"
from the slider buttton.
We recommended not to change the code because if you change the code then while updating to our new version all your customisation code will be lost. So better make child theme and first unhook the functions and the edit the code.
http://codex.wordpress.org/Child_Themes
The file is insidetheme folder -> inc -> structure -> header-extension.php
Thank you