1. Open iTools and connect the iPhone to the computer with a data cable. Click Advanced Features, and then click Clean up Garbage. At this time, iTools will automatically clean up the Program Backup Cache and the Photo Thumbnail Cache.
2. If you want to clean up thoroughly, click the crash log option that appears in step 1, use Ctrl+A of the keyboard to select all, and then press Delete to delete all.
3. if the iPhone is still short of space, you can go to settings > general > usage, check the space usage, and then delete unnecessary or unused applications and games.