need more space

[Kenzo]

need more disk space
This is a two part question.
I'm running FBSD4.8

1. when I do a " df -hi " I get.
> df -hi
Filesystem Size Used Avail Capacity iused ifree %iused Mounted on
/dev/ad0s2a 126M 119M -2.6M 102% 2676 13578 16% /
/dev/ad0s2f 252M 14K 232M 0% 8 32502 0% /tmp
/dev/ad0s2g 21G 2.6G 17G 13% 196822 2580776 7% /usr
/dev/ad0s2e 252M 20M 212M 8% 1144 31366 4% /var
procfs 4.0K 4.0K 0B 100% 30 1014 3% /proc

telling me that my / slice is pretty much full.
How can I tell what is part of the / slice so that I can find what is taking
the space and delete things that I don't need.

2. would it be better to try and find what is taking all the space or just
grow the slice with growfs?
Can I make the /usr slice smaller and give some to / or can I link the
directory that's taking all the space in / to somewhere in /usr?

Thanks.