its very easy I had the same problem transferring files and downloading apps.
Just go into settings>storage check and swipe across to details and go down to clear temporary files. Somehow all files and apps downloaded are stored hear as well (Microsoft need to change this, bit of a pain)
Hopefully that will do the trick (I know it's a bit tedious if you are repeatedly downloaded lots of files and apps)
Sometimes it takes awhile before it will let you clear the temporary files. One trick someone came up with was advancing the date by a month or so on your phone and then going in an trying to clear the temp files. Then going back and setting the date back to the correct one. It does not work all the time; but it has worked for me a time or two. Worth a shot, what do you have to lose? My temp files are holding at 52MB, and my Other storage at about 400mb. Us poor AT&T phone owners still have not received the GDR2 update that is suppose to help this out. I have been with AT&T for the past 8 years; but when my contract runs out I am a gone Pecan. Hope this helps you out. fdalbor
Here is the tip: IF the temporary files takes too much space (it normally takes 50-100mb) than you have to erase Internet Explorer history. Go: meniu - IE - function (...) - settings - delete history. NOW you can delete your temporary files: ) It should clean this memory.