How can I update my direct deposit information with turbotax?

[NCperson]

you can do it when you file your 2020 tax return

if you are asking because of the stimulus, the IRS does not permit changes due to the risk of fraud. 

[DoninGA]

You can enter your bank routing and account number for a direct deposit of a 2020 tax refund in the File section of the program on Step 2.