If you have entered the list box options as a "value list", then you can't
update this in the table and reflect the changes in the form(s). You can
either go into design view on your table and copy the list, then open your
form in design view and paste it into the properties box for the control.
Or you can delete the control from the form and then re-add it.
Using the manually-entered list is not very useful if that list can change.
A better way is to add a new table for all the options and then pull the
values from the table. This also means that non-Access programmer types
will be able to go in and edit the table of valid entries and the changes
will be reflected in all your forms.