You can download the program from here: http://www.autohotkey.com/download/
I skip the installation guide cause its basically hitting the next button. When it asks you to make example script hit Yes. It opens notepad which should look like this:
Delete everything and write in scripts you want to use and hit save:
This one changes your mouse's side button to alt and your alt to 0
Now you should have application running in system tray, right click and Reload this script.
You'r new scripts are now ready for use! Remember, its not permament. You can easily switch back to original buttons just by closing AutoHotkey.
Thanks for reading!