This wikiHow teaches you how to delete your Telegram account and all conversations in a desktop web browser.
Steps

Step 1. Open your internet browser
You can use Chrome, Safari, Firefox, and Opera.

Step 2. Enter the Telegram account deactivation page
Type my.telegram.org/deactivate in the address bar and press the ↵ Enter or Return keys on your keyboard.

Step 3. Enter your phone number in the "Your phone number" field
You must enter the same number that you have associated with your Telegram account.
- Make sure to include the country code at the beginning of the phone number. All codes begin with the sign " +".

Step 4. Click the blue Next button
They will send you a text message to your cell phone with a confirmation code. Enter the code on the computer to deactivate the account.

Step 5. Enter the confirmation code in the "Confirmation code" field
Look for the alphanumeric code in the text message on your cell phone and enter it here.

Step 6. Click the blue Login button
If the confirmation code entered is correct, you will be redirected to the "Delete account?" Page.

Step 7. Click the blue Done button
It's at the bottom of the screen. In this way, your Telegram account will be deleted.