can we upgrade iphone sdk 3.1 to highrer level?

can we upgrade iphone sdk 3.1 to highrer level ?so that i an use new released frameworks or i have to download lates开发者_如何学运维t sdk to use the new api

You have to download the latest sdk as there is no option to update sdk. So download new sdk and install it to use iOS4.

You can download new sdk and install it but you have to check your ios version first. If your ios version will support new sdk version than you can upgrade it.