On windows 8.1,
Skype app file transfer is done by temporary copying those file in appdata of current user
suppose, user name is bhushan so this is path to my data on local machine
Then SendingStorage is for files you are sending and ReceiveStorage are file receiving
completely received files are stored in Current user\Downloads by default
If you encounter disk full because of large file sending failed,
Option 1: You can just delete those files from SendinfStorage folder.
Option 2: Move your appdata location to other drive having large disk space
you can relocate appdata by mklink command, but this command is to be executed while you are not running windows,
Run windows using bootable DVD or going into repar menu and command prompt.