how do I delete the update MacOS Catalina

Why do you want to do that?

Maybe if you post an Etrecheck report we can help you with solutions to your problem.

I suggest you use the program created by Etresoft, a frequent contributor.  It will provide a snapshot of your system which we can analyze to possibly determine the cause of your problem. Please use copy and paste as screen shots can be hard to read. On the screen with Options, please open Options and check the bottom 2 boxes before running. Click “Share Report” button in the toolbar, select “Copy to Clipboard” and then paste into a reply. This will show what is running on your computer. No personal information is shown.

https://itunes.apple.com/us/app/etrecheck/id1423715984?mt=12

Use the Add Text button to include the Etrecheck report in your reply.

That's a slightly glib answer although semi correct. In a number of cases, eg my 2017 imac and 2012 MBP, when you erase a patition with Catalina on it, that partition becomes an unusable unremoveable partition of 'free space'. The only solution for me was to erase the whole HD (having ensures a backup of the other partition(s)) and start again - without this troublesom OS.

Too many issues with this OS at present I will reinstall once a couple of upgrades are offered by Apple

Restore your backup from prior to upgrading.

Yeah, never jump on an upgrade before you really need to. :)