You could use a double boiler or microwave
Heat it up very slowly.
They make a pot that looks like an old fashioned coffee pot for making candles. I have a wax melt container for scented wax that I have used to melt a broken candle to make a votive from it (I reused the wick).
I use a double boiler but you can DIY your own with a pot inside a pan of simmering water :)
Use a clean empty can smaller than the saucepan Put water in the saucepan, and the wax in the can. Heat over a low heat and watch carefully.