upgrade my iphone 3gs

hello , please any one can help me how to upgrade my iphone , 3gs ios 6.1.6 to ios 6.1.3
Answer #1
Aint gonna click the link….
Dont know why this post even needs a link :/
FYI you cannot ‘upgrade’ your iPhone from iOS 6.1.6 to 6.1.3
Answer #2
reply please