To update personal details in the Paytm app, users can follow a few straightforward steps. First, they should open the app and log into their account. Once logged in, users need to navigate to the "Profile" or "Account" section, which is typically accessible from the main menu or via their profile icon. In this section, users will find options to edit their personal information, including their name, email address, and mobile number. After making the desired changes, users should ensure that they save the updates to commit the changes. Depending on the specific updates, users may be asked to verify their identity through an OTP or other verification methods. If any issues arise during this process, it is advisable for users to check the help section of the app or the Paytm website for additional guidance.