I don't know what the maximum is but there is only 1 memory slot. The computer was fine with 4 but I removed it and installed an 8 GB chip which cost $40 from Amazon. I think if you use the Crucial memory configuration tool, you will only see a 4 GB and 8 GB chip as options. You can also get the part number and look it up on Amazon.
The Yoga 13 has a single memory slot. It takes a 204 pin SO-DIMM. The memory is DDR3 speed is 1600MHz (PC3 12800). At the present time the largest available single stick is 8GB. The i5 an i7 processors support 32GB but the motherboards may not, so it is not clear if larger expansion will be available when (if) 16GB DDR3 becomes available. For now assume 8G max, which is more than enough for this machine unless you're editing video or something... which you probably ought not be doing with a 17W TDP processor with built in graphics.