If no bleed valves are fitted. Then the only option is to open the radiator plugs at the top of the rads but be very careful and screw the plug back as soon as water shows!!! Are you certain that bleed points are not built into the radiators?? SOME ARE!! Check the back of your rads. Good luck.
all rads have a bleed point somewhere try lookink @ the back as some makes have it there (ps if there is a little plastic plug prize it off & bleed point will be behind)