HTC one m9 factory reset how to keep whatsapp and contacts?

[AC Question]

Hi I have a HTC One M9 and I want to factory restore my phone due to slowness and lag and whatnot. Anyway before I do that I want to keep all my whatsapp conv and contacts. How do I do that? Do I need to install a program first? I am not tech savvy so I'm really noob lol. I really appreciate the help

 

[B. Diddy]

Welcome to Android Central! Before you do the reset, have you already tried a cache partition wipe, which won't erase any personal data? https://support.t-mobile.com/docs/DOC-20857