Is it possible to use the free space on my Data drive on my C drive? im pc illiterate!?

i have 144 gb C drive and 144 gb Data drive. i dont know which drive is used for what, and my C drive has very little memory left on it. i am wondering if there is a way to somehow transfer the space on my Data drive to the C drive, since it appears all 144 gb are free on the Data drive. please be kind when you answer, i'm not an idiot, just computer illiterate!