You will probably do a better job than the professionals! Here's what to do:
Remove all TRV heads and set all wheel valves to full open
Close (turn clockwise, like a tap) all Lockshield valves then open 1/2 a turn
(The head of a wheel valve may fit and make it easier)
Set pump to speed 2
Set system to heating only
Turn up room stat to a high temperature (so the boiler does not go on and off)
Let the system warm up
(If you have an infrared thermometer or a meter which measures temperature use that, but if not your hand will do)
Check the temperature of flow and return at the boiler - they are your guide. There should be a noticeable difference.
The task now is to adjust the lockshield valves on each rad so they all have the same difference.
Start by feeling each rad: the flows should all feel he same but the returns may vary considerably.
Open up the LS valve of the rad with the coldest return by 1/12th turn or less
Wait 10 minutes for the change to take effect
Check each rad and open the coldest one by 1/12th turn or less.
Repeat until you can't tell the difference between one rad and the next.
You should frequently check the difference at the boiler (a) to refresh your memory (b) to make sure it is not increasing/decreasing too much.
If the boiler difference decreases a lot set the pump to speed 1; if it increases, set pump to speed 3.
When satisfied (don't expect perfection!), replace all TRV heads and adjust wheel valves as required.
Set room stat to required temperature.
