It’s actually pretty straight forward and shouldn’t take long, but I can see how just looking at the links to functions can seem a bit confusing. I’ll outline the process step by step so it should be easier to follow.
First off you will need to create a Child Theme. We offer the frameworks free in the store so download the relevant one for the SP theme you’re using (i.e if you’re using Default theme, download the Default Child Framework).
Next you will want to copy the head template (spHead.php) from the parent theme’s ‘templates’ folder to your child themes ‘templates’ folder. Assuming your forum is the one on the website associated with your username then it looks like you’re using Default theme, so the path will be wp-content > sp-resources > forum-themes > default > templates > spHead.php.
Then you’re going to want to open your newly aquired child themes spHead.php template in an editor or the SP theme editor (WP Dashboard > Forum > Themes > Theme Editor) and locate the function ‘sp_RegisterButton‘ on line 94. As the Codex states it has a ‘link’ argument for adding your own URL, if you were to add it in the function would look something like:
sp_RegisterButton('tagClass=spButton spRight&link=http://www.yourlink.com', __sp('Register'), __sp('Register'));
So you can replace the entire function with that and change the URL to be whatever you need, and when you click the register button that’s where it will take you.
Hope that helps!