Q: best cleaner software

Very slow Air. Please help!

I have a macbook air version 10.5.8

Speed 1.6 GHz Intel Core 2 Duo

Memory 2GB

Bus Speed 800MHz

It takes several minutes to start - say 5 mins.

When opening each app it akes a very long time

There is freezing and much spinning wheel of death.

However when looking at Activity monitor there:

System momery syas 2Gb free

Disk usage says 50 GB free

Don't know why so slow

Please can anyone help?

Am not very tech literate. Please can any fixes be kindly described..

Best