Starting with version 12.0 of the Mobile Impact Platform, it is possible to change a field type directly from the designer's user interface via the field type properties panel. The best way to illustrate this is by way of example. In the screenshot below, a form is designed with a field named "Percentage":

By clicking the "Change field type" link at the right, the designer is presented with a list of other types. In this case, they'll choose a Masked Edit field type:

The resulting field has been changed and the designer has updated the mask:

Field type changes will attempt to preserve information if possible. In the screenshots below, a radio button group is changed to a drop down list. Note that the items in the drop down list correspond to the previously available radio buttons:

Also note that if you attempt to change a field to a type that is much different (e.g. a drop down list to an image annotation), you may be prompted with information regarding validations and report bindings if they are not compatible with the new field type as shown below: