Help with inspiron 15 3558

I bought this dell laptop and i would like to know if i can add more memory to it. 

I searched for the spec manuals (i.e. Inspiron 15 3558 (with optical drive) Specifications )but the ones i found do not match exactly the specs of my laptop. For istance mine has i7U cpu and geforce 840M as a couple of differences.  

So my question is can i upgrade my ram (my laptop only has 4GB or ram atm)? Up to a maximum of 8gb? 

How many ram slots my motherboard has?  

If it has two slots what is the exact specs/make of the ram so that i can buy the exactly same one? 

Thx for your time