Rear suspension mech creaking

It's hard to say exactly what it will involve without having taken apart that particular bike before. First I would try to find exactly what is creaking.

Undo the top of the shock and rotate it away from the rocker. Then you can move the rear suspension and see if you can produce the noise. If you can, it's the pivots not the shock bushings. If fitting one end of the shock and rotating the shock around it causes the creak, it's the shock bushings. These are often the first to wear, particularly the end that rotates more - in your case the top of the shock. See here for how to replace: https://www.youtube.com/watch?v=3VQ1M5_C7JE

If it's the pivots, you may need to replace some bearings - order a bearing kit from your local merida dealer. Fitting can be a fairly length job and can require suitable tools to remove and re-fit bearings,

As sounds can often seem to be coming from locations other than the actual source, I would also try removing the seat post, cleaning and regreasing/carbon assembly pasting (depending on materials) it and the inside of the seat tube. Then replace and check the torque/QR force on the seat post clamp. Also do the same with the bar clamp, steerer clamp and saddle rail clamp, as these are common causes of creaking that are hard to distinguish from suspension. Cranks and BB are another possible cause though you can rule this out by bouncing the bike with feet off the pedals.

Good luck!