If you're worried that you might not be able to make the next payment on an installment loan for bad credit you've taken out, the first thing you need to do is contact your lender right away. While the terms of most bad credit installment loans are strict, you may be able to renegotiate the payment schedule if you are honest about your situation.
Remember that you're ultimately responsible for paying back the money you borrowed, and your lender isn't obligated to accommodate any special requests to keep you from defaulting.