Question RAM Upgrade Advise (Acer Aspire M3970)

Sep 4, 2019
Hi there poor gamer here,
I am here to ask for advise and enlightenment on my ram upgrade. I currently own an Acer Aspire M3790 which I bought years ago. My current ram is 2 GB DDR3-1333/PC3-10600. I would like to ask:
1.) Can I use this 2GB in tandem with a new ram I am eyeing to buy which is a 4GB DDR3-1600/PC3-12800 (YRUIS or RAMSTA which is the only RAM i've canvassed so far in the nearby stores)? I'm planning to buy one at first and then buy a second one later to replace the 2GB for a total of 8GB if it is compatible.
2.) If it is compatible, which is more preferable Ramsta or Yruis, or is there a better brand with the same specs?
3.) Should I strictly stick with 1333Mhz/PC3-10600? It is hard to find 1333MHz, most stores sell only 1600MHz.
4.) Any further recommendations?

Here is the link for the spec of my PC:
Chipset Model:
Current Ram: UNIFOSA HDDR3-1333 2GB 256MX8