You're not eligible for an upgrade.
The service need to be at least 7 days old, and usage need to be at 75% of the initial allotted space.
As for deleting of unnecessary files, ONLY delete files you uploaded/created. Anything outside of /domains/DOMAINNAME/public_html is system related, unless you are sure it is a file/folder you created or uploaded, and should remain intact. The only exception being that you can remove files from INSIDE the .trash (using the empty trash bin feature seen at the bottom of the folder tree is safest), this folder would only be visible if there's actually something in the trash bin though I believe.