If you want to transfer a domain to HostUpon follow the steps below.
1) First login to your client area here: http://www.hostupon.com/hosting/clientarea.php
2) Once you are logged in click on Order Additional Items
3) Then scroll down near the bottom of the page and click on Order Domain Registration Only
4) Now you can choose the domain transfer radio button and proceed to the order form and pay for the domain transfer.
Note: Domain transfer can take anywhere from 7-10 days and your domain must be unlocked at your current domain registrar.