Are you talking about a Home Equity Line of Credit? If so, many HELOC loans come with a feature that allows you to convert into a traditional home-equity loan at some point. I.E., after their draw periods are up, many HELOC loans allow you to convert them to regular home-equity loans. This will provide you with a fixed interest rate and a fixed payment instead of the traditional adjustable interest rate that you get with a home-equity line of credit. You should contact your lender.
One way to get a fixed rate is to refinance your mortgage. Good Luck!