Stop playing Lee Sin and Rengar, start conforming to the meta until you're good enough to not. Lee Sin is TERRIBLE in Bronze, and even though you have a decent KDA with him, it shows in your 48% W/R. Pick a role you like best (Jung?), pick 5-7 champs for that role. Then pick 2 secondary roles with 3-4 champs available. Then learn the last two with 2-3 champs in each. Obviously you'll have your pref for every role but you need to be able to play multiple due to bans/picks.
Make your picks EASY champs. I don't care how good you may think you are, if you're in bronze with nearly 300 games played you aren't good, end point. So what you should to do to fix that lack of game knowledge/exp/whatever it is? Pick the easiest, most flavour of the month carry hard champs, and keep conforming to that meta. You'll find some champs you haven't played before and like, and some you don't, but this essentially forces you to learn new champs and increase your champ pool.
So basically:
Narrow down your pool based on primary roles/secondary.
Pick easy champs that are strong in the current meta.
Learn more about the game.
Also:
Increase your cs. On your midlaners you have horrific CS, under 100 for Fizz and 130 a game for Zed. Given how long bronze games usually go, thats an awful, awful rate. Increase that and you win games by simply outfarming the enemy laner. You don't even need to kill them, just harass and try to farm every single creep.
Ward more. You upgrade your trinket which is REALLY good for your elo since most people don't. However you don't buy wards. Start buying pinks early, and stealth wards before you can upgrade.
Watch pro's and videos detailing the little things. Lane advice/ganking paths/etc.