1 The use of the lumia software recovery tool is the most safe way to do it.
2 There is another method but than you need to flash your rom and that i would not recommend because you need "experience" and if you do it wrong you brick your phone.
3 You could go to a Nokia service center maybe they could do it for you.
4 With a hard reset you can not go back to cyan. You stay on pfd
5 You do not to roll down to get denim, unchecking the box in the app is enough to get Denim
If you need more info please register and reply on this post.
Many have reduced battery, inefficient WiFi and other glitches on P4D. Some want to travel and desire the stability of Official. Maybe the OP wants to go from Official to the TP. I'm not sure it matters why for one specific individual, does it? Maybe they are getting ready to sell the device...