You can easily upgrade your Yoga from 4GB to 8GB. It takes a little care, but it can be done.
But if you are upgrading to get more video graphics memory (more memory, more to share?) you are going to be disappointed. It's all about sharedvs.s dedicated memory. I tested with GTA IV to see if I could get it to run. I did, but the results aren't because of the extra memory in the system. That video to follow.
In the meantime, here is a video with the exact instructions, including a close-up of your keyboard tabs and the precautions to take when removing the keyboard to install the memory upgrade.
As far as which memory to buy, be careful and read reviews. There are some manufacturers that have had a significant amount of failures. So be careful on your selection. Also make sure you have the proper speed of ram for the Lenovo. A low price may hide the fact of lower speed ratings or a history of failures.