I have a base model 2018 Mini. I would like to upgrade from the stock 8Gb of RAM to 16Gb. As far as I understand it, it would be better to buy 2 8Gb sticks of RAM and throw away the 2 4GB sticks that are in there now, is that correct? Buying 1 16Gb stick and keeping 1 4Gb stick in there would end up being slower, right? Second, Can anyone recommend which RAM to buy and where from? I am in the US and have an Amazon Prime account. I don't know anything about RAM so I really need someone to tell me what to buy lol. Thanks.