The most bang for your buck changes to your bike are as follows.
position change: if youre able to get more aerodynamic by changing the cockpit without losing comfort, this is the fastest change for your money.
tires: faster tires will be a bit faster
wheels: faster wheels will be a bit faster, but less bang for your buck than tires.
roadies swear by tires called “gp 5000” and while they are a marketing gimmick and absurdly overpriced, they are still a “cheap” option if you want to buy speed. Start with that and being more aero.
wheels are usually considered more worthwhile to upgrade than changing other components that aren’t mentioned to be more lightweight.