The column Properties window displays properties for an individual column. If you open the column Properties window from a Data Grid, you can make changes to those properties.
If the words read-only appear after the name of the data table at the top of the Data Grid, then the table is in read-only mode and you will not be able to make changes. To switch to update mode, select Data Read-only from the menu bar. This toggles the data table from read-only to update mode.