How do I erase all old programs using the new scratch type Education software?
The LEGO Education Website EV3 firmware update page lists two options.

Use the EV3 Device Manager web page. The instructions are not entirely clear, but if you visit the web page with Chrome (recommended), Safari, Edge, or Internet Explorer, click the Available Bricks (0) button and wait a very long time, it will eventually pop up a dialog asking to download and install an EV3 Device Manager program to your computer. The EV3 Connection Manager program runs in the background on your computer and communicates with the EV3 Connection Manager web page in the browser. After installing the separate background program, the web page will be able to connect to your EV3. Then you can use it to update the firmware. It does not appear that this method gives you the option of selecting which firmware file to use. It will likely give you v1.10E, which has some known issues (EV3 acts as USB mass storage device which doesn't always work, and on-brick data log app is missing). But that version should work fine for most uses.

If you have Windows, Chromebook or older macOS (10.14 Mojave or earlier), you can also install the older software and use that. It is available from the LEGO Education retired products download page. (Android and iOS versions might not work due to lack of USB connectivity needed for firmware update.)