How to replace door frame from termite damage?

evidently there are termites at the top of the door frame. i found out when i tried to open the front door and the top plate ( i think that's what its called) fell off. can someone give step by step instructions on how to repair/replace this problem, or direct me to a DIY site that can help. unfortunately i... show more evidently there are termites at the top of the door frame. i found out when i tried to open the front door and the top plate ( i think that's what its called) fell off.

can someone give step by step instructions on how to repair/replace this problem, or direct me to a DIY site that can help.
unfortunately i cannot afford a contractor to fix it, luckily i will have help to do this.
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