These examples assume you have read Accessing the Full API.
If you need to retrieve the bio, biography or about information for a user you should use GetFullUser:
from telethon.tl.functions.users import GetFullUserRequest full = client(GetFullUserRequest(user)) # or even full = client(GetFullUserRequest('username')) bio = full.about
See UserFull to know what other fields you can access.
The first name, last name and bio (about) can all be changed with the same request. Omitted fields won’t change after invoking UpdateProfile:
from telethon.tl.functions.account import UpdateProfileRequest client(UpdateProfileRequest( about='This is a test from Telethon' ))
You need to use account.UpdateUsername:
from telethon.tl.functions.account import UpdateUsernameRequest client(UpdateUsernameRequest('new_username'))