You would open the table in design view and change the field type, but a
date is stored in the table as a number. If you change it to a text field
you will end up with a pretty much meaningless field.
If you want to display a date in a different FORMAT, then you can do so in
your forms, queries, and reports. For example...
=Format([SomeDateField],"medium date")
or
=Format([SomeDateField],"long date")