Adoption conditions

25 years back parents of 5 year boy child expired in an unfortunate accident. Child was brought up by one of my friend who was just married then and was close relative. Subsequently he got  two sons.

Now he wants to adopt the grown up boy, legally to regularise his upbringing at par with other sons and also to ensure guardianship..

What is the best way ?

Thanks for feed back in advance.

Regards