Rebuilding My Blog

I’m rebuilding my Blog from scratch: many old posts are going, some categories are going, the template is been changed, I am making major changes. In reality it will look and feel like a new blog.

My ‘new’ blog I have sitting on my test site https://www.mytestsite.com ready to go, I’m satisfied that I have got the look and feel right, and that my links and such like are in good working order.

Now my question is this. What is the best way to post all that is in https://www.mytestsite.com into the ‘original’ blog ie. https://www.myOLDblog.com

As you can guess from above I want to completely overwrite the files in the original blog.