When you try to copy files from your hard drive to an external device such as an external hard drive or USB stick, you may get an error message saying that there is no free space left on your device, even though you just deleted everything to make room. This is most likely due to the limitations of the file system your drive uses - newer drives may already be using the NTFS file system, while older ones still use FAT32 or even FAT16.
The problem is that FAT32-formatted drives only support files up to a maximum size of 4 GB. For example, if you try to copy an image file of 6 GB to an external FAT32-formatted hard drive of 320 GB, of which 100 GB are still free and not in use, the copy operation will fail. To change this, you need to format the destination drive to the NTFS file system.
Formatting will erase all data on the drive, so back up everything you have on the drive first. Then right-click on the drive in your file browser and select Format.....
In the window that appears, the File System drop-down menu will probably show a FAT file system (if it already says NTFS, this guide won't solve your problems). Before you change anything, double check that you have selected the correct drive. Then change the file system to NTFS and click Start.