Scaling unity sprite sheet for different resolutions

Unity Engine
1

How can I scale down a Unity2D sprite sheet that contains multiple sliced sprites to support different devices. For example HD and SD. also I want the SD version to have less physical size than the HD one.

please let me know if there are better approach to follow.

2

Mipmaps?

3

Thank you for your reply, so is it enough to turn mipmaps on to use lower resolutions spritesheets on small devices? and if you could please explain how the memory will be effected