Can I upgrade my iPhone5s to an iPhone 6 for free?

I currently have an iphone5s and it is so awesome, but after hearing the recent ios8 release, I want to upgrade my phone. I think the newer the better. After all, technology is improving.

Is it possible? And is it free?

Yes, everything is free.
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If by upgrade you mean get a new phone, yes, you can absolutely upgrade your phone if you're eligible for an upgrade through your carrier.

Is it free? Of course not. The cheapest iPhone 6 will be at least $200 with a 2-year contract. If you are not eligible for an upgrade it will be full price at about $649.