How to restore ipad without enough memory?

If you are attempting to restore a backup to a device - and the backup is larger than the available memory of the target device - the you’ll not be able to restore from the backup.

This scenario would suggest that you are attempting to restore a backup that did not originate from the device to which you are attempting to restore. Whilst it is technically possible to restore a backup to a different device, the target device must have adequate internal storage to accommodate the data contained within the backup.

The backup cannot be selectively edited.