The D Minor melodic scale, like all melodic scales, has a different set of notes on the descent than it does on the ascent. Climbing up the scale you have D, E, F, G, A, B, C sharp, and D. Coming back down you hit C, A sharp, A, G, F, E, and D. Now let's take a look at the fingering.
Start off the scale with the thumb of the right hand on the D. After the third finger hits the F, bring the thumb under to hit the G. You'll end up with the pinky on the D octave. Coming down, remember to hit the C natural and the A sharp, but otherwise simply reverse the process to get back to the original D.
The left hand starts with the pinky of the left hand and works up to the A with the thumb. From there, bring the third finger over to hit the B and finish out the scale. Your thumb will end up on the D. Coming down, remember again to hit the C natural and the A sharp.
Practice the scale until it is second nature, and remember to also keep practicing all of the other scales that you have learned up until this point. Scales are the very foundation upon which music is based, and the more you know, the better.
Next, you can practice the E Major Scale.