if you are in login-mode, the files you are looking for is either /etc/bash or /etc/bash.bashrc if you are in non-login-mode, you are looking for the file /.profile or for the files within the directory /.profiles.d the files mentioned above if where the system variables are.
This is only if you want the settings to be system-wide, which is probably not the most common use case.
Leading or trailing colons should never be used, and the current directory should never be in the path.
After trying every suggestion under the sun but /etc/environment, and having them all NOT work, i finally stumbled across this. The variable values are usually stored in either a list of assignments or a shell script that is run at the start of the system or user session.
In 7 and 8, the variable value for Path is nothing more than a long string of text with various locations around the system. Once you’ve clicked the edit button, a new dialog box will appear with each location in the path on a separate line.