Article in English: It's a red app with a white triangle in the middle. Doing so open's your YouTube main page if you're already logged in. If you aren't signed into YouTube, you'll need to tap ⋮, then enter your email address and password to continue. It's the circular image you chose in the top-right corner of the screen. This displays a drop-down menu. If you have not uploaded a profile image for your account, your profile image appears as a colored circle with your initial in the middle. This option is near the top of the page. If you want to change the name of an attached channel, instead tap Switch account, tap the channel's name, and then tap the profile icon again. It's on the far-right side of the page, directly across from your username. This is the pencil-shaped icon to the right of your current name. To do so, replace the names in both the "First" and the "Last" text fields with your preferred name.  You must enter a first and last name if you're changing your username. If you're changing a channel name, this field will simply say "Name" and it will not require a "Last" section. It's in the top-right corner of the screen. Doing so changes your username, which is the name people see when you comment on videos.  This name also appears in Gmail and on Google+. You can change your name three times every 90 days per Google's policy.

Summary in Vietnamese:
Mở YouTube lên. Nhấn vào biểu tượng kênh nằm ở góc trên bên phải màn hình. Nhấn vào mục My channel hay Kênh của tôi gần phía đầu trang. Nhấn vào biểu tượng nằm bên phải trang, ngay cạnh tên bạn. Nhấn tiếp vào biểu tượng hình cây bút chì nằm bên phải tên hiện tại của bạn. Đổi tên. Nhấn ✓ hoặc OK ở góc trên bên phải màn hình.