front sprocket

Hi All, I've been browsing the site and appreciate that you guys are here to help out hacks like me. I've taken on a bike and everything is going well so far based on what i've browsed on this forum but now i'm going to get into the details that I need to ask! (still have charging, ignition...

I am trying to replace the front sprocket without removing the heads, etc. Any words of wisdom that will help?