...
At the beginning, you must find the Contract, on which you want to change Financing rate. On dashboard click on Active and choose the concretely Contract.
...
Step n. 2
Then you will see Financing Card. Click on button Process and Change Financing Rate Wizard.
...
Changes you made are also shown in section Process, concretely in Calculator Lines and Payments Calendar.
...
Follow up:
How to change financing period
How to change principal amount