You can make all or some of the columns in a table updatable.
Updatable columns are displayed highlighted. Click a nonupdatable column to make it updatable. Click an updatable column to make it nonupdatable.
If you have changed the updatability of a column, you should change its tab value. If you have allowed a column to be updated, you should change its tab value to a nonzero number so you can tab to it.