Hard Disk Partition

hi ,

I have a partition of linux which is 40GB in /dev/sda4 and a 40GB
in /dev/sda5. I created it when installing Fedora Core 3. In /dev/sda5
i have my /home partition and I have 3 users . Many data is there in
/dev/sda5. I want to get the 40GB from the /dev/sda4 combine with
/dev/sda5 without losing data.

Can any one tell how is to be done in linux . I think it can be
done using partition magic but that is in windows . So any help would
be appreciated .

Pai