Make sure you get the correct type of memory.
The current memory will be in the screw off bit underneath where the hard drive is
The slot for the new memory is actually under the keyboard and it's a pain to get off, but be careful.
There are about 5 small tabs around the edge of the keyboard, which you have to 'gently' lever to get the keyboard membrane over them.
It then lifts off and you slot the memory in