An example of defeating higher ratings
Here's an exciting game I played against Fins0905, an IM here on chess.com. I believe there was definitely an element of luck on my side here, but I believe it also illustrates some important points about having a chance of defeating a higher rated player.
The keys for my win here were that I played in a comfortable opening, not trying to move it into some obscure sideline that would lead to an incredibly difficult position where he could likely outplay me positionally. Instead, I played very aggresively, forcing moves and building up a lot of pressure on his position until he made a mistake, which I was then able to take advantage of. Play the sharpest and most comfortable chess you can or you really don't stand much of a chance!
In general, tips to keep in mind:
1) Play comfortably in your own style, don't do weird moves because you think they're weird
2) Don't be afraid to play several book moves i.e. don't go into obscure lines or play novelties that you really don't know in the hopes of surprising your opponent.
3) When in doubt, play aggresively and tactically. The other person can likely outplay you positionally (that's why they're higher rated!)
4) Realize that they are higher rated for a reason, but don't go in expecting to get totally crushed and play your best chess.
5) Realize that you have no pressure on you to win and if you lose, no one will think any less of you. In truth, your opponent has all the pressure to win because who wants people knowing you were upset by someone 600 points lower than you?