as above memtioned, after installing iOS-6, my iphone-4S is slow in running, such as can't open mail, camera and sometime stop.
how can i slove it, do i need to restore the last version.
There is no supported method to downgrade the iOS.
Before leaping to silly conclusions... try basic troubleshooting from the User's Guide.
Basic troubleshooting is reset, restart, restore (first from backup then as new).
Retrieving data ...