If you can see both the small and the large hard drive on your PC, then open Windows Explorer and browse to the files you want to move to the new large drive. Select all of the files that you want to move, right click on them and select 'Cut'. Now browse to your new drive and then right click and select 'Paste'. This will move the files from your original small drive to your new larger drive.
You can select multiple files by holding the 'Ctrl' key on your keyboard before you left click on them. Once you have several selected you can then do the right mouse click and select 'Cut'.