Go to your Unity 2018.4 installation folder. (If you are using Unity Hub, go to your Unity Hub installation folder instead) then go to Data\UnityExtensions\Unity\GUISystem. Replace every files into this folder.
In an Image component, if you are using Sliced ot Tilled you will see that no option adjustment for PPU of your sprite. But in 2019.3 or greater, they had implement the PPU feature that able to adjust PPU in Image component. (But you need to downlaod via Package Manager)