These are generic thumb rules for any circuit and hold good for SRAM also
1. If the same devices available in the new technology, the aspect ratios are kept same. In the other words, shrink the geometry by the shrink   factor. Change the mult factor of the devices if the new technology has limitations in max width.
2. For the devices which are there in old technology but the new technology's foundry doesn't have it, you need to look for closest device characterstics (through simulation) and compare the device strength with the desired aspect ratio. Extend it for resistances, metals etc.