Since you are only dealing with files and not the OS you can simply copy the files to the new drive.
Open the drive in My Computer, Press Ctrl + A to select all files and folders and then right click on a highlighted file and select copy. On the new drive right click and select paste.
Do the same on the other drive. Now if any files or folders are the same then you will need to decide which one to keep.
Note if you have programs installed on either drive they will not work without fixing the shortcuts and registry settings.
You could also make two folders on the new drive, one for each drive, and then copy the contents from each drive into the respective folder. This will avoid copying over files.