if its the type of beam the elements telescope on, then it might not be that hard to convert for 6m.thats taking into account you no longer wish to use it on 11m.
for 6m centred on 52mhz you would need to make the driven element about 8.98 feet (2.74m) total length.reflector would be around 9.44 feet (2.88m) and director would be around 8.54 feet (2.60m),if your tubing will telescope into those lengths you've cracked it.
after that the only thing you would have to worry about is spacing between the elements to give the right impedance,trial and error with an antenna analyser preferrably or a swr meter if its the only instrument you have would optomise the beam on the new frequency range.
as others have said though it may be more desireable or easer depending on the 11m beam design to build one from scratch and keep the 11m beam for 11m or 10m or build 1/4 wave gp which is simple and relatively small for that frequency range.
Infact if you made the radiating element of the 1/4 wave gp half the size of the above lengths for the beam driven element,4.49 feet or 1.37m you wouldn't be far out,add 3 or 4 ground wires of the same length at 45 degree downward sloping angle attached to the coax shield and you got yourself a very cheap and very effective 1/4 wave groundplane for 6m.
might be wise to add a little extra to the lengths to allow for tuning the antenna in its mounting location.