Upgrading and Templates

I have WordPress 1.something (the most recent before the newest). I just installed it, but I don’t know if I should upgrade it to 1.5… I’m still a beginner with PHP and it took a while to edit the index.php to my liking. Should I upgrade?

Also, is there somewhere that I can get the default template for index.php? I removed the sidebar but I’d like to put it back. Thanks ??