Gas boilers often (usually always) have an operator control to set the temperature the water is heated to - Set too high risks the overtemp thermostat tripping so mid position is best. If your boiler also heats domestic hot water and you set the control too high the tap water may be uncomfortably hot and might scald the young and old.
Circulating pumps often have a speed adjustment to control the speed the water is pumped around the rads - set it to a higher position to get the heat distributed around the house more quickly.
Radiators sometimes collect trapped air and only heat at the bottom - need to be bled from time to time to let the air out. Radiators hot at top and cold at bottom suggest sludge build up in the system and it may need cleaning out.
Radiators have two valves the inlet and outlet. Very often the outlet (lock shield valve) is fully open and should not be. All available heat is used up by the first few rads and the rads at the end of the flow only see luke warm or even cold water. Rads may need to be "balanced" to adjust the flow through each rad for a 10 degree centigrade (18F) fall between inlet and outlet. Search on here for "balance radiators" for techniques to do this simple job.
Peccavi, December 2008
