You can install BT5 over the Ubuntu partition, but it is recommended to re-create the partition. You can leave the swap partition untouched.
You might want to use gparted (is in teh BT5 DVD you burned)..Open up a terminal and type gparted. Erase the Ubuntu partition and create a new one with ext4 filesystem. Apply changes
Then just install the BT5r3.
Luck..


