Hi. I have a .deb file that my archive manager tells is constituted by two files: control.tar.gz and data.tar.xz

I want to replace data.tar.xz by data.tar.gz. So I extracted data.tar.xz, which resulted in three folders: etc,lib and usr. I compressed the three into a single data.tar.gz.

Then I used my archive manager to open again my .deb file. Then I was ready to delete the data.tar.xz and replace it with the tar.gz.

However, the option to delete it, was disabled, as the option to add files.

So, How should I proceed? Do I have to create a new deb file from scratch?

what is your archive manager at all?
In any case, would be better to create a new deb package instead of "repairing" it.

deb is an ar archive and ar supports all basic operations including file deletion.