Update:
Sorry, I for some reason though you were asking if it supported up to 64GB.
it supports up to 32GB of ram but unfortunately, I would not recommend putting two different sticks of different sizes and most likely different speeds and timings together as this can result in nothing working at all or causing issues that lead to failing hardware. you need to buy your ram in kits.
For a 16GB kit I will recommend you this one. it's on sale for the next 23 hours it says but I think newegg might be lying about that
https://www.newegg.com/Product/Product.aspx?item=N82E16820313771
Otherwise, can you provide the model number of the current 8GB stick you have and we can look up a link for it and provide that to you since you can also purchase an identical stick to the one you have mostly likely for less than a new kit and they will go together and work properly