How can I edit a json file with Construct 3?

I am creating a game that loads its levels through a json file, and I would like to keep the changes that occur in it. But I can not find a way to edit the json file.

Can anybody help me?

In the project tree right click Files -> New -> JSON

Once its added as a file to your project you should just be able to double click the file in Construct 3 editor and edit it there in a spreadsheet view.

If you want to keep track of changes that happen in runtime (for example, when player opens a chest), you can't save them back to that JSON file. But you can save them into an array or dictionary and write it in Local Storage. Or simply save the entire game state using System-Save action.