Resized Partitions

I do have a Win 98 SE, I replaced my Hard Drive from OEM 13 giga to a 20 Giga HDD, my computer is working just fine (Software and Hardware, but I am using just 13 Giga (Drive C: 7.39 and Drive D:4.68), how can I resize the partitions?
I restored my back up from the Old Hard Drive (OEM 13 Giga), please help.