TL/DR: We are going to install the official executable for dwebp, if you do not want to waste your time just https://ezgif.com/webp-to-png.
Webp is a very small image format provide both lossy and lossless, where you may happen to get it when you drag an image to download.
Official Website
Mac
If you are a mac user, you can also try using my Drag and Drop dwebp script:
https://gist.github.com/jimmyctk/c246cb9d64e2058b07a75ef1434d2475
Simply execute it, and it will ask you to drag and drop the files you want to convert, and Press enter, volia!
Pre-requisite
If you are running on Mac, you got 3 ways to install dwebp:
1. Install via homebrew
brew install webp
2. Install via MacPorts
sudo port selfupdate
sudo port install webp
3. The hard way (which I wont go through)
https://developers.google.com/speed/webp/download
Windows
I have also another bat file to Drag and Drop:
https://gist.github.com/jimmyctk/18dcb0c49cadbbd9c41663bedab13b07
dwebp.bat "C:\path-to\dweb.exe" "C:\path-to\file.webp"
Pre-requisite
- Download the executable
 - Decompress the file and put the folder somewhere nice
 - Press “
Win+R” and typeSystemPropertiesAdvanced, Enter - Open the option 
Edit the system environment variables - Click 
Environment variables...button - There you see two boxes, in 
System Variablesbox findpathvariable - Click 
Edit - a window pops up, click 
New - Type the Directory path of your 
.exeorbatchfile ( Directory means exclude the file name from path) - Click 
Okon all open windows and restart the command prompt