While it is a good practice since forever to keep user homes on a separate partition, lately this single filesystem has become a trend I see. probably because of big disks.
Anyway, you can "merge" the partitions. First you need to get rid of /home mount. means you need to log-off all non-root sessions and open a root one. then create a /home.tmp or something and
cp -a /home/* /home.tmp
to copy the /home content into it. then
if its says the fs is busy, check
lsof -n | grep home
and kill any process still using it. now swap the home.tmp and home. I have no idea if ubuntu still uses /etc/fstab, but I assume it does. remove the /home mount from there. now you can re-login or even reboot and use gui tools to try and
oh my... why is / partition AFTER the /home ??????? What did the installer's author smoke to allow it?
sorry dude, scratch the above. you cant "grow" partitions backwards. you need to move things. The only way to do that is with an unmounted / fs. means you need a livecd or something. to boot and manipulate the partition table off-line.
Feel adventurous? While it is doable, most probably you will end-up reinstalling that precious ubuntu. Chances are you still have little if none customizations on it so you can just start it all over choosing the partitioning scheme suits you best.