hi my ipad 2 home button dont function because the screen is brooken can i change it for an ipad mini?

No. Even if you were going for 'in kind' exchanges, you can't exchange a broken ipad 2 for an unbroken one. YOu especially cannot exchange a broken one for a 'free' upgrade.

(there is a caveat, iwth iPad 3 and above you could have purchased apple care plus and taken advantage of accidental damage repair and had two instances of exchanging a broken device for a refurbished replacement for $49)