RAM upgrade

Short answer, yes you can.

Leave the 2 4 GB in their slots and add the 2 new sticks to the empty slots, that's it.

The question is though, do you need 24 GB of RAM, are you doing a lot with the Mac?

 

You do not have to have 4GB sticks for all. But for best performance you should install them in pairs (as OWC recommends) to take advantage of dual channel support. So, in your scenario, of having 2x 4GB and 2x 8GB would be fine.

 

Just look if you have pageouts in Activity Monitor, if you don't have them you don't need more RAM.

 

Pageins are not so important, this is data read from the HD/SSD, example, any file, App opening is reading from disk.

Every computer has physical RAM, now, that RAM is limited by its size, as soon as it is all taken the System needs to write it to Virtual Memory which is on the "Slow" HD/SSD, the more it needs to write to it the higher the pageouts.
Pageouts are cumulative and only a restart will clean them out, remember that RAM memory is 0 when you shutdown the computer, it is volatile.

If you have lots of pageouts more RAM is needed to prevent the System from slowing down.
Sometimes people think that the more RAM you have the faster the System gets, this is not true.
Example, you have 4 GB RAM and have pageouts, the System is slower, you buy/install 4 GB extra, no more Pageouts, the System is behaving normally, now add 4GB again, this does not make the System faster since you didn't have any pageouts and it will not make the System faster, you would have wasted money by installing the last 4 GB.

The best you can do now is to monitor pageouts for a week or so, restart every day (Or two) and see if you get pageouts fairly soon after restarting, if that is the case you will be helped by installing more RAM.

By what I see you don't really need 24 GB, 16 would probably do the job, but this was just a snapshot, you just have over 1 GB page outs, this tells me it wasn't too bad but maybe you had many more before, therefore it is fairly hard for me to say if you are OK with 16 GB or need more.
Most of the time, for "normal" Users which do a bit more 16 GB is sufficient, only the "real" Pros need more than that.

 

This is a perfectly fine configuration. And from what you said, more memory will improve your performance.

However the price difference between an 8GB kit and a 16GB kit isn't that much and would leave room for growth. It's up to halfmonkey to decide if they feel like the extra memory is worth it or not.

 

Good point, I just left it out, thought he could think of that himself.

 

i have 20GB in mine. i just bought the 16GB upgrade because it was so cheap. i don't really need it.

 

Wasting money then, better give it to me.