You may choose to install this software onto a storage device/disk sector apart from your system partition (the hard drive area containing Windows system directories).
Note that; in this case please ensure you have at least 3 GB of free space on the system partition. Like other Windows based software, DesignSpark Mechanical has dependencies like the Microsoft .NET framework which require storing some of its setup configuration files on the system drive/partition.
Suggestion: You can run the "Microsoft Disk Clean-up" which helps remove unnecessary clutter from your system drive and free up significant storage space;
Right-click the system drive and open 'Properties ->Disk clean-up'.