It is best to contact your loan servicer about changing your repayment plan. However, you might want to use the Loan Simulator to get a look at which plans you may be eligible for and see estimates for how much  you would pay monthly before contacting your loan servicer.
I have not been able to make a couple of loan payments in the last months and am wondering what I should do about it?
If you have missed some of your payments it is best to contact your loan servicer and explain your situation especially if you are struggling to make payments on time.