[ALUG] Hard disk drive partitions and memory

1) Noticing that this PC gets glacially slow occasionally (it probably means get a new one and soon but bear with me for the moment) I had a look at the hard disk. 77 GB is 84.4% full. I have two partitions though. One 'extended partition', the other a swap partition. Both 3.1 GB. Could I unmount the first (extended partition) safely? 2) What is it full of and how could I clear stuff out, again, safely? Bev. (braced for the worst.)