Variables can be given a new name at any time. Double-click on the variable, and enter the new name.
Renaming a variable in “List of document variables”
Renaming a variable is possible at any time and does not affect the variable’s stored values.
Deleting a variable is done in the same way as renaming it.
Select the variable you want to delete with the mouse. Now the focused variable
is highlighted in green. Then click the Delete
variable 
button in the
toolbar. When you delete a variable, the whole column including all its values
will be removed from the table.