These links may help explain and guide you through the process.
https://turbotax.intuit.com/stimulus-check/ link to stimulus registration (SR). It is very important that you uses this link that says register now if you don't need to file taxes this year. Otherwise, you will not be able to E-file a zero return. It also has the calculator.
The IRS says it is working on developing a web-based system for people to give the government their direct-deposit information. Keep checking www.irs.gov/coronavirus for more details on this.
Edited 04/07/2020
I filed taxes with a tax preparer who works with a company that gets all of their refunds direct-deposited into their accounts and a check printed and giving it to us. will the government send my stimulus check to them or will they mail it to me because it's a company
This is a work in progress, so I'm not sure which would happen. You can follow this link and change it when it's available.
If you only want to change your Direct Deposit Information
The Treasury is expected to shortly announce an online portal where direct deposit information can be supplied to the IRS. Here is what you should do:
Go to http://www.irs.gov/newsroom/economic-impact-payments-what-you-need-to-know to see if they have set up the online portal. (This article will be updated with the web address once it’s available.)