use the repositories if you're new to ubuntu/linux in general.
sudo apt-get install thunderbird
Basically you have a file /etc/apt/sources.list that contains a list of URL that tells your ubuntu installation that it can find software there.
You update the versions listed by
sudo apt-get update
You can upgrade all installed packages by issuing
sudo apt-get upgrade
You can search for specific things with
apt-cache search KEYWORD
You can even use pipe and grep to narrow down things
apt-cache search editor | grep "command line"
Get to know apt better by issuing
that's a very short man page but it lists the apt related programs:
apt-cache(8), apt-get(8), apt.conf(5), sources.list(5), apt_preferences(5), apt-secure(8)
onto which you can each individually run