If you are in India there are about 500 million people who will claim to be experts and able to help you 😉
Have you had a look inside the box – see what’s in there, take out a stick and post a photo – probably 2 of 4 slots used so you will have some options. When I have done similar in Mac I found older chips (slower clock speed) where more expensive but newer ones worked. Also a single 8gb stick was cheaper than 2×4 – as you say a single 4 maybe cheaper than 2×2. Any 2gb’s lying around you can snaffle for free ? (I gave a friend an unused 2gb chip you may find similar)