Changing a field's type will change at least one of two things – how the field looks and how the field behaves. This article only covers how to change the field type and doesn't explain the different fields and how they work, so you may want to check out our other article: Understanding the different field types.
To change a field's type
Select the individual field that you want to change by tapping on the field's prompt. This will display configuration for the field along the right-hand side, like this:
The first configuration option is the field's type. Tap on the drop down to choose something more suitable. You can scroll through or start typing to search for the desired field.
Whatever field type you select will be reflected on the field itself to the left and will give you different options. For example, a select-list type question will give you space to put options in:
The other field configuration settings include the field visibility i.e. when the field should be displayed (more on visibility logic here) and whether or not the field is required (if it's displayed).
After making any changes, be sure to Save your changes and Publish your form to make it available on your iPads.