In either your .bash_profile or your .bashrc files. You generally have generic files in your /etc/skel directory, and every user has them in thier user directory. They're hidden files, as that's what the '.' in front of the name does, but you can see them with 'ls -A'
cat /home/username/.bash_profile should show some of your path (the $PATH part is based on your startup files in /etc), but there might be additional settings in /home/username/.bashrc