Storage Space for Trial Version of Norton Online Backup

I am into my 4th day of using the trial version of online backup.  I am only allotted 5G of space.  I need at least 10G.  How can I purchase this additional space without buying the full version?  How can I fully test this product without backing up my hard drive?

 

I tried using Nathan for this information.  But he does not understand my needs.