Answer

- Go to Settings
.
- If you have Automatic Graphics Quality enabled disable it.
- Now select graphics according to your needs.
More info about settings here - http://en.tankiwiki.com/Settings
If you don't have any graphic option there then Enable Hardware Acceleration http://en.tankiwiki.com/Hardware_acceleration
Customer support service by UserEcho
Make sure that "Mip mapping" option is checked.