Download "latest version"

I know I saw a thread on this before, but now I can't seem to find it! Can someone point me to the modification needed to allow purchasers to download "latest version"? I'm getting ready to add a new eBook to my site, and I can almost bet I'll have changes between now and sometime next week, so I'd like purchasers to just be able to log in and get the "updated" version when available.

Thanks!

Danita

if you are running 1.4.8 or newer this is built in now.

Oh - very good! Yes I'm on 1.4.8. I see 1.4.9 is also available now, so I might upgrade that - I was just half-way through all of my modifications on 1.4.8 when I noticed that :-)

Danita