As you can see to the left TreeSizeFree is showing that there are 20.6 GBs of data being stored in a folder called System Volume Information (SVI). By default this folder will be hidden so you must first show all hidden system files with either a CMD prompt or PS prompt this can be done quite easily.
CMD
dir D:\ /AH
Get-Childitem -Force
Next type "vssadmin list shadowstorage" to find the loaction and size information of the SVI folder.
vssadmin list shadowstorageAfter you know the location of the SVI folder you can change the MaxSize of the System restore files
vssadmin resize shadowstorage /For=D: /On=D: /MaxSize=5GB
From 3% to 12%.