how to increase /tmp size

[LinuxSoul]

hi
i have ddserver RH9
uploading server for files mp3s etcs

my users can't upload big files them get error in upload coz my tmp size not big

i wana increase my /tmp size to 5 Giga ex,
soo how can i do that
i try fdisk /dev/hda*
i get this error

Unable to open /dev/hda*

i dont know how to fix that
plz some one help me fast

[Javasnob]

I assume /tmp is on its own partition.

I would use gparted or qtparted. They're graphical frontends to parted, a partition editor.