if you open up 'computer mangement', which is found in the start menu, you can then open the 'snap in'..... Storage. It's here that you can right-click on the partition you want to remove and make the necessary changes.
There may be a third party program that can do it, but most , even Acronis, one of the best, can be unreliable as far as saving your data, is concerned.
I would suggest you move all the "data" (You may have to examine exactly where you are gonf with that, if you have two identical OS's installed) on to the first partition. Make a directory which you could call, for example, "saved"
Then go to the disk management function and dlete the now, unwanted, partition. Go to the previous, active partition and stretch it entirely into the old, now empty, space.
You will then be free to select and tansfer data as you wish.
One word of warning. I have no idea how or in which order you installed both Os's, but remmebr that the boot MBR will be on, and associated, with the last installaton.