How to choose RAM?

Laptop model
Acer Aspire e5 575g-54ZH
Initially, two strips of RAM, 2GB and 4GB capacities(from the store)
CPU: Intel Core i5 7200U
How to choose RAM for this laptop?
How to know the frequency for this model laptop?
And what characteristics do you need to choose RAM(Without volume)?

And is it possible to put on this laptop model DDR4?