Access makes it very easy to change the data type of a certain field; simply open the table containing the field you want to change and pick a new Data Type from the appropriate row.

However, you must take care when modifying a data type in a table. If the field is in a relationship with another table, or if the output of several forms and reports depend on the one field, changing the data type can be a major task. You can examine the dependencies of an object by selecting the object in the Database window and clicking View à Object Dependencies. Objects that depend on a particular object and all objects that a particular object depends on are visible by selecting one of the two radio buttons at the top of the Task Pane:

As you can see, the Categories table has quite a few objects relying on it! Modification of this table could end up being a long and tedious task. It might even be faster in some instances to scrap the Categories table altogether and design a new one with the modified data type.

If you feel you have to modify a data type, be careful and make sure it is absolutely necessary to do so. Remember that you should always make a backup copy of the data base and/or a copy of the object itself before you make any big changes, just to be safe.