Recent versions of Internet Download Manager (IDM) have been updated to detect download files that exist in IDM temporary folder (which no longer necessary for the user) and asks the user to delete them when IDM was updated to a new version, with a dialog like below:

‘IDM has found unreferenced and not deleted parts of old downloads in IDM temporary folder. C:\Users\<username>\AppData\Roaming\IDM\DwnlData\username\ Would you like IDM to delete them to free your disk space?’

Without any hesitation, you can click ‘Yes’ and allow IDM to delete those files or  you can do that manually also, here is how.

1. Visit %appdata%/IDM/DwnlData in Explorer or use Run dialog command

2. Click on your username folder

3. Select and delete all files.