Presumably your are attempting to restore the iPad to factory settings - which requires a fresh copy of the most recent version of iOS/iPadOS supported by your iPad to be downloaded from Apple's servers to your computer, where it will be unpacked and verified prior to being transferred to the connected iPad.
The error that you see relates to the computer with which you are attempting to restore your iPad. The Hard Disk - or at least the Disk Partition that is being used to download and unpack iOS/iPadOS - has insufficient space to complete the operation. Until such time as you create adequate free-space on your computer, you'll not be able to restore your iPad.
If you are unable to resolve the problem, the technicians at the Genius Bar of your local Apple Store or Apple Authorised Service Provider (AASP) will be able to assist with restoring your iPad to factory settings - after which you will be able to restore your data from an existing iCloud or iTunes backup.
Genius Bar Reservation and Apple Support Options - Apple