Changing a profile field checkbox from vbadvanced

[Vitesse]

Hi guys, got a quick question

I'm looking at setting up a mailing list on my site and was planning to have say a submit button from within a template. What i effectively want to do is check to see if the logged in user has got field 5 in their profile checked (checkbox) and if not then check it and save the change. What is the best way to do this as my coding isnt great by any means.

Edit: Should have been a bit more specific about this really, i'm using vbadvanced portal, created a cusom module and want to have a submit button in that module that when clicked by the user will change field5 checkbox to checked in their profile.

Thanks