Williams chief technical officer Pat Symonds says the team needs a bigger budget in order to become competitive again.
The team improved last season after new sponsor Martini came on board and Symonds believes they can go even further in 2015.
He said: "I think the step from third to first will be harder than ninth to third, I really do.
"The potential has to be to win the world championship and there is no point in doing anything else.
"What will it take to do that? It will take a lot of hard work and it will certainly require a larger budget than we have now.
"I don't think it is necessary to have a budget like Red Bull or Ferrari's – I believe you can do better with less – look at the fact we are operating on a budget half of Ferrari's and we beat them.
"But ultimately, that is the only reason I have taken this job on: I want to win another championship before I go and sit on the beach.