There are 2 ways to change a folder icon permanently. Here is the step by step tutorial:
How to change folder icons in the standard Windows way?
First, you should select and right-click the folder
Secondly, select Properties from the drop-down menu
Thirdly, select Customize tab in the dialog
Then click on Change Icon… button
Select an icon from the suggested list
And change the icon by clicking on OK and then Apply button
Hem. Six steps to change a folder icon are too many!
Hopefully, there is one small utility that can do the same in a very different manner than Windows, actually in ONE click, and users will have a better choice of options and icons. The utility is called Dr. Folder and it can be downloaded at https://www.pcclean.io/dr-folder/
How to change folder icons in the Dr. Folder's way?