Hot Water Tank Temperature Control

[zingo1327]

I had a new standard Worcester Bosch gas boiler fitted.I also have a hot water tank and the fitter fitted "stuff" to it and set it to a temperature of 60 degrees. Because it is too hot I want to reduce it to 50 degrees but the wheel under the digital display doesn't alter the desired temperature regardless how I turn it or push/turn it. Anyone know how to fix this before I try getting the installer back out? thank you in advance

[Togo]

There should be a thermostat mounted on the tank itself (perhaps hidden under a lagging jacket) turn that down and it will tell the boiler to stop heating when it reaches your set temp.