When creating a new field /column in a table (either existing or a new table), one must select Tables > Add Field from the menu bar. One has to then populate the Name (mandatory), caption (optional), Type (need to select the appropriate choice of what kind of data would this field have from the available list of pull down), look up (optional), Rules (optional), Default Value (optional), Description (optional), Units (optional), and Color (can be set as None or select the color from the drop down list).
After creating the field properties for that particular field or the column, if the TYPE property needs to be changed, then within the INPUT tab, one would assume to right click that field name/column name, select Field properties OR one would highlight that column, go to the tool bar on the top, select Tables - Field properties to get the same dialogue box. Either ways, when trying to change the 'Type' field, it appears to be greyed out which suggests that any editing is not possible.
How would one achieve this?