I'm creating a form and I'm trying to change the payment from paypal to square. It won't let me click on any other payment option.

You can only have 1 payment processor on a single form. You need to delete the existing payment field in order to add a new one. 

In the Form Builder, select the payment field and then click the "Trash" icon.

After deleting the payment field, you can then add the Square payment processor with the help of this guide: How-to-Integrate-Form-with-Square.

Hope that helps. Thank you.

Thank you!!!