Message: Hi, I’ve not figured out how to delete an entry (KantuX) in order to be able to enter new data.
Here are the steps:
Text to change: type
Click - Double-Click (Highlight).
Click and Type Text ${KEY_DEL}.
Type new text: qwerty.
Hi! You were very close to the solution. You only need to add more KEY_DEL or KEY_BACK commands 
This screenshots explains it:
In this example I click in the middle of the input box (= the pink rectangle), so i need both, KEY_DEL and KEY_BACK special keys to delete everything. I use 20 of them in each line to delete longer text reliably (too many are not a problem).
The code in the Javascript field is document.getElementById('ContactName').value="".
Here is a screencast of the macro running: Input Boxes (Forum)
