While running JkDefrag I noticed that there are many WER report files. Windows Error Reporting files are located in your profile folder (C:\Users\<user>\AppData\Local\Microsoft\Windows\WER). There are Gigabytes of these files that noone really needs. To remove them, use DiskCleanup utility in Windows so that they are deleted properly.
The same utility can be used to delete older restore points and free some additional space provided you need the later and not the former.