To download head over to https://notepad-plus-plus.org/
Once downloaded you will be able to open any text document with Notepad++. To do so, find the file you want to edit. Right click on the file and click Edit with Notepad++. This is shown below.

Notepad++ will now open up the selected file.

Notepad++ offers many different syntax highlighting for different file types. As an example, if a python file is to be edited.

Notepad++ will pick up that is is a .py file and will use the appropriate highlighting. If it fails to do so, you can select it from the language drop down menu.

https://i.imgur.com/WdhGF8C.png

Find Replace

Using CTRL + F you are able to find and replace mass entries at the same time.

https://i.imgur.com/nBBTJ7o.png

Using the Replace All feature would turn this:

https://i.imgur.com/BZ6LLGy.png

Into this:

https://i.imgur.com/L0uE7AF.png