EmmRag18

for your purposes replacing one with the 8GB stick would actually slow you down.
the APU is heavily depending on Ram speeds not on Ram size so having unequal ram modules prevents you from using dual channel and gaining band width.
what you want to do is get faster Ram and if you can also some more of it but generally this will not do much you are better off getting a faster CPU/GPU.

Well if you want 
Cooler master and their MWE lineup is pretty good 
Be quite and their psus are decent
And ofc the legend seasonic