Replying to Ipod problem (sorry)

hey sorry to make another itunes thread but i need help fast

ok so my total library has only 2.25 gb of music in it, i deleted all my playlists so all there is is library, but it says that my ipod does not have enough free space for the songs even though it is a 4 gb ipod which should have more than enough space right? i dont know if maybe i have to clear my ipod and then update it..if anyone could help out i would apreciate it a LOT...thanks.