You can set the Fullscreen scaling property from high to low as a system action.
You can use the sprite action load by url.
Or you can make a duplicate layout with the low resolution textures.
The system memory management tools can also be of use.
The latter three are most likely more work than it is worth, when you could just design your game with appropriate specifications for your target device in the first place.
Also note that lowering texture/vram use won't get you "better performance" anyways, depending on how you define performance. If your game is running slow in terms of fps, Vram usage is probably not your problem.