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Morgan's men are through to the semi-finals after beating New Zealand, but have the chance to put Australia out.
"If we're going to be contenders, we need to beat the best and Australia are one of the best," said Morgan.
"So to go in to a game like that with no other attitude than winning is very important to us."
England will go through to the semis as Group A winners regardless of the result against Australia, but Saturday's clash could be the final time the two sides meet before this winter's Ashes series.
New Zealand will also be looking for England to do them a favour, as an Australia win would send the Kiwis out.
In Cardiff on Tuesday, England posted 310 and looked under pressure when New Zealand reached 158-2.
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But after Mark Wood found extra bounce to remove Black Caps skipper Kane Williamson for 87, it began a collapse that saw New Zealand lose their last eight wickets for 65 runs.
"We batted OK," said Morgan. "We weren't that pleased at halfway and thought we were maybe 20 or 30 short of par.
"The guys did the right things, but it doesn't always work. But, when you post over 300 you're always in with a shout."
In an all-round display from the England side, four of the batsmen made scores in excess of 48, while all five bowlers used took at least one wicket.
However, the form of opener Jason Roy remains a concern. The Surrey man, who had not passed 20 in his previous seven ODIs, made 13 before being bowled by Adam Milne.
Morgan, who has previously backed Roy to remain in the England side throughout the tournament, said: "It doesn't change very much.
"We'll obviously have a chat about the team, but, certainly within a winning side, it's very hard to make changes going into a game where you don't really have much to lose."
England captain Eoin Morgan says his side will show no let-up when they meet Australia in the Champions Trophy at Edgbaston on Saturday.