How To: Change the data type for an existing field
Instructions provided describe the steps to transfer data from a field of one data type to a field with any data type desired.
Sometimes attributes are stored in fields of a specific data type with limited capabilities, for example, math functions cannot be performed on text fields, because integers do not store decimals. While it is not possible to change the data type of a field, there is a way to get the same results.
In ArcMap, right-click on the name of the feature class whose table is to be modified and select Open Attribute Table.
In the attribute table, click the Options button and select Add Field. Enter a name for the new field. Set the data type and its properties. Click OK.
Right-click on the new field and select Field Calculator. Then double-click on the name of the field whose data type is to be changed. Click OK.
Note: When converting from a text field to a field with a numeric data type, remember that the text must have numbers and no other characters, except decimal points.
The new field now contains the data from the previous field, but it is stored as a different data type. Delete the old field, if necessary.