Bleeding the air from rads is for removing the air or hydrogen from them.
Yours is leaking water. You are going to have to close off the lockshield valves at both ends, then drain the water from the rad, remove it and work out where the leak is coming from. The two most likely places are: -
1) its has rusted through from the inside and pinhole leaks are appearing. Remedy - a new rad.
2) one of the joints is leaking - either where the threaded pipe is screwed into the rad, or between this threaded pipe and its connection to the lockshield valve. Remedy - re-attach with the ample dose of PTFE white tape.
A keen DIYer can do this job - but you may have to call a plumber if you ndon't feel confident to give it a go.