To delete your Telegram account, you'll need to head to the settings menu. It's pretty easy to find - just tap the three lines on the top left, then Settings, and finally Privacy and Security. From there, scroll down to Account and tap Delete Account.
Now, here's the important part: you'll need to enter your phone number to confirm it's really you who wants to delete the account. Don't worry, it's a quick and painless process. Just type in your number, and Telegram will send you a confirmation code to make sure you're not a bot trying to cause trouble.
