I'm not sure I understand your question.
I'll assume that you have 2.5 GB free space on a 500 GB drive. If that's the case, your drive is actually full. Windows needs some extra space for system restore, the page file, and the hibernation file. You need to free up some space either by deleting unwanted programs data. You can run the disk cleanup utility. For optimal performance you need to keep something like 10% of your drive empty.
If that is not possible, you will need to add another hard drive or upgrade to a larger drive.