how to speed up macbook

Hi, my Macbook is 3 years old and I feel it´s getting slower and stalls when editing or flipping between programs.

It has 2 GB memory and Mountain Lion isntalled. I only run standard programs like iMovie and iPhoto. I try to have 40 GB free harddisk as I noted that with less I start getting trouble.

I guess there has gathered some digital dust over the last 3 years and that is what makes it slower. Or is it just that the later program versions demand more capacity)

Is there any way I can make my Macbook faster?

Thanks in advance for helping.

seakjell, Varberg, Sweden