how do you carry games?

not a troll question. first i want to say I main jungle. i play a lot of rengar, and i just wanted to know how do i properly carry my team? people tend to say "in order to get out elo hell u need to carry your team" but i just find it impossible to solo carry. there's many strategies the enemy team can use to counter a solo carry, too many to write down.

i find myself having games like 19/2/18 or 21/2/5 and yet not being able to win. i start off pretty good, most of the time i get first blood and im in a good start. but then when my team mates start feeding and then all lanes feed im like "wtf do i do now?".

then all of a sudden mid, top and jgler are fed af, and there's nothing i can do. at this point two things happen from here. I either get shut down by one of the fed players from the enemy team, or the enemy team decides to group up. and having the higher gold and level advantage we just get destroyed in a 5v5....and i still get shut down.

how do i carry?