Can't add data to USB memory sticks

[Weeler]

   I have a couple of USB storage devices ( 2GB and 4GB). I've got about 55Mb already on my smaller
one and 200Mb on the larger. But now when I try to add new data files. (Jpeg, .xl, wp....whatever,
a window comes up telling me "unable to create file on USB drive J".  The drives were 'formatted' when I
first installed them.....and I loaded the data I have on them all at once. Now I'm trying to "ADD" more data
and they won't accept it. So basically I have devices with a LOT of space that I can't use. When I look at
the properties box, the pie chart shows me I have 3.8Gb available, and 1.5Gb respectively.
   To me it sounds like a formating or 'partioning' issue. How can I get around this....with out 're-formatting'
and losing all the valuable data I've got on them???  Someone help step me thru the process.
Thanks so much!!!!!

[Computer_Commando]

Copy the data from the flash drives to your computer's hard drive, now it's backed up.  Try to format the flash drives.  You can use this to format it.

[Sodde]

Computer_Commando's advice is the right way to go, just be careful that you format them to a usable FAT (file allocation table). I would suggest FAT32 instead of FAT as there are less limitations in using the device.

One other thing I've come across is when you try to copy lots of separate files to or from a thumbdrive in one operation, it will error or not complete. I've had success with putting the files into a folder first and then copying the folder over.

[Weeler]

Thanks to both of you for your assistance. Your process worked nicely. I thought they were already formatted
properly. Guess not.