As an admin or manager, go to "Timecards" in the top navigation, and click on "View" next to an employee's name. From here you'll see their timecard, and you can edit individual punches:
If employees are allowed to, they can also request changes on their timecards. As an employee, click on "I need to change something."
From here you can click on "Edit" next to a punch time. Note that your administrator has the ability to allow edits. If you don't see the option, then they've disabled it.