To change a field's type in Marketo, please follow the steps below:
Log in to Marketo and press the Admin tab on the right upper corner:
Press on "Field Management" on the left bar:
Search for the field on the right bar and click on the field:
Press "Field Action":
Choose "Change Field Type."
Choose the required field Type
*Please note that a field with the type of "Score" can not be changed to any other type.