Problema installing Crucial RAM on IMac 21.5inch

Hi there
I just bought an 8gb pack from Crucial to upgrade my IMac to 12gb.
I watched a tutorial and the first thing i noticed is that the two RAM memories that are already installed, are on the top slots (with the IMac screen faced down) when in every computer ive seen is the other way.

Anyways i tried to pull the tab to take the old ones out, and wasnt able to do so!

I ignored that and continued, and when i tried to put the new ones in, they just wont fit!

Help please!
This is very frustrating

You didn't mention which 21.5" iMac you have? Year?

The memory slots on the 21.5" iMac are very tight (I have a 21.5" 2011 iMac) and require considerable force to seat the modules. The same goes for releasing the modules.

Also, the modules that are already installed are correct. They should be in the top slots (with the iMac face down) and not the bottom slots. All new iMacs come with the top slots populated. Additional modules go in the bottom slots.

If you bought the memory from Crucial, it's the correct memory. Make sure you're putting the modules in the right way (they will only fit one way). Push down hard with your thumbs (use a soft cloth or gloves) until you hear a slight click, then continue to push until you hear a second click. The module is seated.

DO NOT REMOVE THE MODULES FROM THE TOP SLOTS. Leave them alone.

Thanks for the quick response!
My IMac is from late 2009

I have checked i am putting them in the right way. I pushed really hard but stopped because i was afraid i could brake them.
All the videos ive seen seemed pretty easy and this is not.
I havent managed to make them click even once.

If you are 100% sure you have the correct memory, there were two 2009 iMacs, all used PC3-8500 modules, download this .pdf from OWC and follow it:-

Performance Upgrades; FireWire USB SATA Storage; Memory, more at OWC