As of June 1, 2010 all free hosting accounts are being upgraded to unlimited disk space and bandwidth.
Therefore it would be a little pointless to order the Double Space & Bandwidth upgrade at this time.
Take a look at Upgrade
and you will notice that this particular upgrade is no longer listed.
There is also a Double Everything package which is currently available:
"For a one time fee of $4.95 we will DOUBLE everything on your free hosting account. (MySQL, Add-ons, Parked, Emails, Etc.)"