What resolution are you gaming at?
There is no "fix" for the VRAM. The GTX 970 is designed by Nvidia to have a 3.5GB and 0.5GB slower ram. That is why there is a significant price difference between the GTX 980 and 970.
The GTX 970 still performs as expected when it was released where the 3.5 gb vram spec was unknown.
If you gaming on 1080p, get either the GTX 970 or R9 290.