Thanks for posting here. There is a way to edit the columns, rows, etc. of an existing table.
You can do this by clicking inside one of the boxes of the table you want to edit, so that the text cursor is somewhere within the table. After that, go to Format > Tables just like you did when you created the table. The small Table window should come up, and you should now be able to change the amount of columns and rows.
If you would like to edit all of the boxes at once (e.g. fonts, colours, border thickness), you can highlight them all with your cursor and then change the settings. Let me know if you need anymore help with this.
There does not seem to be an option to delete a single row within the table. Removing rows will delete the last row only. I'll let the team know about this, as it would be a useful enhancement. I apologize for any trouble this may have caused you. Let me know if you have any other questions and I'll be glad to help out.
I have been able to remove a single row in a table by highlighting just
that row or rows if more than one, then choosing Edit > Delete
Paragraph. However, it does not seem to be possible to undo that action.