While using source ~/.bash_profile or the previous answers works, one thing to mention is that this only reloads your Bash profile in the current tab or session you are viewing. If you wish to reload your bash profile on every tab/shell, you need to enter this command manually in each of them.
If you use iTerm, you can use CMD⌘+Shift+I to enter a command into all current tabs. For terminal it may be useful to reference this issue;