hard drive partiton problem

I have a total of 40 gb hard drive and i have them in two parts one is in 19.53GB and is FAT32 format and the other is in a as a logical drive and not formated yet it has 17.73gb in it free the other only has 3.13gb free and i want to find out how to use the other part of my hardrive that is not yet formated as one big hard drive without re installing windows because i dont have a windows install disc and is it safe to do anything?