How to change middle of Apple Watch face to show date and time?

There is no way to change Watch faces except for what is available in the Watch app on the iPhone. I have no idea what older version of Watch face you are referring to, so it is difficult to see what could be what you are looking for. Except for some of the analog Watch faces, most of the digital faces have the date and time more in the corners of the Watch face. You can provide feedback to Apple letting them know that you would like to see a Watch face like you are asking. Use this link. Feedback - Watch - Apple

When you open the Watch app on your iPhone, there are 2 different places to look at Watch faces. The first is when you have My Watch tapped on the bottom of the phone screen, which then shows you My Faces at the top of the screen. There is an Edit button there also so you can set your personal Watch faces. It you tap on the middle button at the bottom of the Watch app, you will see "Face Gallery". There you can go through all of the available Watch faces you can get, including the complications you can use on each face. You just need to select a Watch face that meets your needs.