As Mark says, this does not make sense.
I assume you mean you have two areas of hard disk (called partitions) not RAM.
Are they called C: and D: for example?
If C is full and D empty then you can move personal files from C to D in a number of ways.
You can use "drag and drop" to drag them from the C drive to the D drive. Or you can use "cut and paste" to move them from C to D. These are fairly easy to do, but hard to explain in the short space answerbank provides.
Note ONLY move personal files (pictures, music etc). Dont move programs or Windows files.
You can get the computer to save things to this other area (which may be called D) by changing the default each time you save a file or files.
So if, for example, you are downloading a load of pictures from your digital camera to your computer then just change the default "C" drive to your "empty" drive (which may be "D" but you need to check).