Please ensure he is also taking Paracetamol
650 three times a day or 1g twice daily to lower the temperature.
It is unusual for acute sinusitis
to cause such high temperatures, so a Chest X Ray is important to ensure there is no other cause such as pneumonia
It appears to have started with a viral infection and super-added bacterial infection is a problem.
If he smokes, he must stop altogether.
Viral infections per se can cause high temperatures, so if the Chest X Ray is normal, continue the Augmentin