Why will my memory not budge?

I have an Advent 7061M laptop bought from PC World years ago (I did beg my dad NOT to go to friggin PC World!) and I want to upgrade its memory, but I'm unable to move the memory in it to see how many slots it has (as I'd ideally like to get 1GB and keep the crappy 256MB that it already has). My theory: PC World don't want people to upgrade their computers! Anyone know why the memory won't slide out with a gentle push like it should?