The ideal temperature range for an axolotl is 58 and 68 degrees Fahrenheit. They prefer it much cooler than most aquarium fish. Keeping your tank in this range is very important to reduce the chance of diseases and stress. Higher temperatures can be deadly to the axolotl.
We keep our main tanks at around 64 degrees F. If your temperature is too low, you risk the axolotl not eating. Extreme shifts in temperature changes can also induce stress. We maintain this temperature very stable by using an aquarium chiller. The brand we use is Baoshishan and it functions to both heat and cool our tanks to a set temperature. Chillers can be quite expensive. However, keeping in mind your axolotl can live to be 10-15 years old, it's worth the investment in our opinion. If you do decide to purchase a chiller, make sure its rated for your tank size.
The other options are to keep your room temperature at this level. However, running an air conditioner all the time can also prove costly. Some people like to use aquarium fans which is probably the next best options. Aquarium fans can be installed at the top of your tank cooling the water surface and they will not cost you an arm and a leg. Other owners use frozen water bottles floating in the tank.
No matter which cooling method you choose, it's always a good idea to keep a thermometer in your tank to make sure your cooling method is working properly.