Is there is trick to winning a game when you win your lane but other lanes lose? Should one roam to help the lanes that are losing? Is it the support? The adc?
Any tips on this would be much appreciated, thanks.
You don't.
In high elo once people give their opponent the kill, they play it safe until they catch up in gold.
In low elo once people give their opponent the kill, they keep playing as if they are not at a disadvantage, and end up feeding extremely hard as a result.
I can't tell you how infuriating it is to have triple my opponents CS, but then get instantly deleted by a 6/0 Annie who decided to pay top a visit.
Let me tell you something that I learned in the tournament I was in the other day (won third place out of thirteen teams):
Roaming really throws things out of whack, and turn games around. Because of teamspeak, every team was using extreme coordination and planning compared to solo queue, so there were less ignites and more teleports. Top and mid lane constantly ganked each other and bot lane, almost to the point that the junglers were the real laners (okay, not really, I did my job and did it well as jungler).
But knowing when to roam is also part of it. I once ganked a lane when I wasn't needed and ended up dying like an idiot, so timing. If you can't roam, keep cs'ing and don't lose xp and gold. If there's an opportunity, go for it.
If you're in top lane, teleport is a great spell to take to help your team out.
As for bot lane, generally bot the adc and support leave their lane to help out (since if they get caught in the jungle, the support can peel for the adc). If the adc can hold the lane, the support can roam to mid lane to help out with a little extra utility (a gank from Leona, for example, can really secure that kill for a midlaner). If you need the tower taken, then the adc should head to that lane.
Also, I've been experimenting and found that 
is a decent item for AP champions to take towers with. It might be a niche, but clever idea for the support to take it and push the tower while the midlaner clears creep waves.
If you are winning your lane help others out.. lol not hard
