Yes you can. IF you use Multiman, you can use the File Manager to move stuff around.
It is located under mmCM tab right under Update as "File Manager/mmOS"
Your USB is DEV_USB000
The destination folder is...
It works like Window Explorer. You can Cut, Copy, Move, Delete, Properties (Checking file sizes like Windows), etc
X is to select one or more items like a left click.
O brings up to the menu like Right clicks
Double X lets you go into the folder.
Square and Triangle does nothing afaik. Pretty basic file manager
The alternative is going onto Multiman XMB and press Triangle while hovering over a game to bring up a similar menu for doing the same thing.
The Copy here will make a 1:1 copy from External and then you would have to delete it off External afterwards.
I would say do the first method with File Manager. You can actually Cut and Paste and you won't have to waste time on deletion since you're moving instead of copying.
In File Manager, use X to select all the crap you want to move to Internal. Use O and Cut them and then paste it into DEV_HDD0/GAMES. Makes a GAMES folder if you don't have it.