TN Visa renewal prior to expiration

Hey there.
I have got a TN Visa last January. I've found a better job though and I need to get a second TN visa. Do I have to go back to Canada or there is a way to do it from here.
What do I have to do with my current TN Visa ? Where and how do I have to
state that I wont be working to this job any more ?

Thank you.

Your current TN visa is only valid for the company that sponsor the TN. The TN is non transferable. You will need to apply at a border crossing to get your new TN with a new company with your new paperwork. When you apply for a new TN, your old TN is no longer valid. No need to inform anybody.