Can I upgrade iMac 27inch 5K Display's RAM from 8GB to 32GB/64GB? I am new with Apple products. i just bought iMac 27 5k, 3.3GHz quad-core Intel Core i5 , 8GB Ram, 2TB Fusion Drive. i wanted to know if it is possible to increase its RAM? i asked the dealer here in Pakistan but they say you can't upgrade the RAM. you will see to send the to Apple USA which will be another expensive story.

I want to know if i can increase its RAM to 32GB or 64GB?

Also what are the good supported ram which was not really expensive but affordable. can you guys directly what kind of ram i need and how to upgrade the ram? i have no idea what of ram i need to purchase online, its so confusing
Yes, you can upgrade the RAM, and have many different options. I bought the very same system you did, and it came with 2 4 GB chips in the four available slots.  I ordered two 4 GB chips for $100 US from https://www.macsales.com, received them 3 days later, popped them in the two open slots and the system recognized the full 16GB; even though the chip pairs are from different vendors, I had no problem with it.

It is incredibly easy to change the RAM on the iMac and MacSales even has videos to show you how to do it. You can take it all the way up to 64 GB. The best way to see if you need more RAM is to open up Activity Monitor and watch the swap space in the memory tab. Under normal circumstances, the only time swap space is used is when the system needs more RAM than is physically installed. So if you see a lot of swap space being used, that means you are using up all the available RAM.

One note: Unix-based systems like Mac and Linux use far less RAM than Windows, so do not compare the two platforms for RAM capacity needs.