The phrase "to free some space" means to remove or clear out things that are taking up room or storage in order to make more available space. Full definition
** The fully installed game requires at least 1.8 GB of free space in your internal storage. (windowspcdownload.com)
We say as long as you have a 20 GB of free space in your hard drive, you can enjoy the pleasure of having both operating systems on one PC. (thewindowsclub.com)
This boosts the amount of free space for most users to 30 GB. (androidcentral.com)