Hi ,
I also use to have a rooster like this and did not have the guts to do it myself actually , I went totally pale by the idea itself first so I also started looking for a new home for the young guy but that is such a sad issue , who wants them if they are male

, sad in fact because nature provided them for a reason , producing babies , yes but other than just having a rooster watching over the ladies and being daddy , what is he ' worth' to us , I totally understand your situation as I had the same experience , with myself , my Rhode Island Reds and ow dear my little girl started to say " stupid chickens no I dont feed them , I dont like them " , that shocked me since I didn't notice it first that weird thing on her leg , untill she went to bath and she started telling me that mister right had been jumping up with his feet and pecking , poor girl is almost a few inches taller than the rooster so I decided to take him to that new home and same old same old , no new home , went by a farmer in the area here who eats lots of rooster

but he began to teach me how since I had / have also lots of very old chickens just like him .
In the case of him being that violent you think about shooting it , how will you be able to get the powder or bullet out without hitting organs ??
Probably , in my opinion not such a good idea , I was tought the following :
in case of agressiveness wait till dark , go catch it as u know where it sits , immediately cut the throat ( arteria ) or you can use the method of chopping of the head but I think that is a bit overdone , a clean cut is the fast way to cull it and let it bleed right away .
They say sometimes that those moslims are cruel etc , no they are not if you see how they cull their chicken , it is the cleanest and fastest way ever , now recently even proven by science . the animal also doesn't suffer since he bleeds out , what is needed also , you cant wait to let him bleed , it has to happen in the first two hours tops and best is ofcourse when the animal is still having warm blood .
After doing that you have now let it bleed , so you can dip into some hot water or ( just a good tip I use ) if the animal is still warm you can already start plucking it and in that last case start with the pinfeathers as they are hard to get off if it is cold , even if dipped into hot water , do not let it in there for minutes , just a ' dive ' into the hot water untill feathers are better to pluck , you will be busy a while ( I still struggle with time in plucking after 12 times ) .
Another tip in plucking : if you hold the animals skin stretched a little bit , not wrinkled etc plucking goes without doing damage to the skin much easyier . and after that you can either first cook the rooster for 15-20 minutes or first remove all the guts etc and then cut it and prepare it but make sure you always have two bowls of water :
you need : 1 with cold water for cleaning the animal ,
1 with hot water since first time plucking can easy take up some time and the animal gets too cold to get the feathers of so you might have to dip it in again .
The cutting is probably explained already thentousand times here so , also since this is long info ( sorry my way of writin is due the english ) I'll leave it up to this , hope you got something on this info !
P.S. : If we love our animals and families we respect it , culling it the most gentle way , securing it won't be shot 89 times lol , is also respect for the animal . Don't feel bad about this , it's nobody's fault and is neccisary ...
kind regards out of Belgium