I need some more Ram for my PC, it's getting a bit long in the tooth but it still does the job (mostly)
Mobo, ASUS P7P55d-e-lx I think, it's got 4 2gb sticks of Ram and I'd quite like to go up to 16gb at least, the cpu is a i7 870, I've got 1 SSD & 2 standard HDDs, I'm running windows 10, mostly used for a large Lightroom Catalog, lots of batch processing. 

I don't want to over invest in this 5 year old PC so if I can find some ram just over $100 I'll be happy. 

can I add 2 8gb sticks and leave in 2 of my 2 gb sticks or should I just remove all of the 2gb sticks? 

TIA, Jason