Read above info, very helpful.
The best way would be rehab where he will get medical/pharmacutical assistance as well as the inability to break down and get some more.
If he is willing at home, you can slowly lower the dose he takes daily to make withdrawl easier.
The time it takes him to withdraw depends on the dose he has used and for how long.
Good luck to you both,
Unfortunately,you can't. He has to WANT to be off of it. If he does,than he could stop cold and go through withdrawal for about a week. If you're there to support him,it will go much easier for him!