It's easy. Just follow the support centre instructions. Make sure you and your work surface are ESD (static) protected. Identify which way round the new RAM module needs to go before you try to insert it. Make sure the clips at the end of the RAM slot pop up fully to indicate that the module has been correctly inserted. Don't disturb the CPU cooler or CPU fan wire/connector whilst you are doing the upgrade. If you need to rearrange any internal wiring (power cables etc.) to access the RAM socket, be gentle with it and ensure that it doesn't snag the CPU fan.
The strange thing is when I did the Crucial test it told me I can install up to 4GB but HP say only 2. Ive got a Compaq Presario SR1619 with an AMD3200 64bit processor 512mb RAM 160 GB hard drive and a 256mb integrated Radeon 200 graphics card. You can see why I need extra memory and there is three spare slots.