Can you log into MY ACCOUNT?
You should be able to select your current service and select either PLAN INFO (Mobiles) or the big CHANGE RATE PLAN (Internet)
However sometimes the options presented don't match what you want, so hit LIVE CHAT and they'll swap you over.
Out of interest what plan from/to are you considering? Are you on month to month now? Are you NBN or Optus?
Apologies for the delay in getting back to you, @Jarred197739. Did you get a chance to speak to someone in this regards since posting? Yes, MyAccount online is one of the options and the other one is My Optus app (for mobiles only) > Main Menu > Profile to change your plan. If you are still facing issues online or need assistance then you can Live Chat with us here. If you need help with anything else in the future let us know. Kartik