is it posible to upgrade my iphone 4 using my computer
iOS: How to update your iPhone, iPad, or iPod touch - http://support.apple.com/kb/HT4623 - If currently using pre-iOS5 you can only upgrade by connecting with iTunes, not with Software Update.
but is it posible to do it from my computer
You've already been given the answer... but let me be blunt.
YES it is possible.
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