I need to update my direct deposit information and my personal cell phone number but I am having difficulty.

Your banking information cannot be changed after your tax return has been filed and accepted.

Banking information does not go from TT to the IRS until you file your 2020 tax return and it is accepted. The IRS will begin to accept  and process 2020 returns at the end of January 2021.

You enter/change banking information in the FILE section before you file your 2020 return. Changing it on the TurboTax site does not do any good until you file your return and the IRS processes your return.   If they manage to start sending  out stimulus checks before you can change your information, we hope the IRS provides a way for you to change it with the IRS.  If your check goes to a wrong or closed account, it will be sent back to the IRS and then the IRS will mail a check to the address on your tax return.

As for your phone number:

https://ttlc.intuit.com/community/account-updates/help/how-do-i-update-my-turbotax-account-information/00/25927

TurboTax does not store your bank account routing and account number.  When completing your tax return you enter the bank routing and account number in the File section of the program.  The bank information is sent with your tax return to the IRS or your state. 

See this TurboTax support FAQ for updating your TurboTax account information - https://ttlc.intuit.com/community/account-updates/help/how-do-i-update-my-turbotax-account-information/01/25927