Yes, you can upgrade using your Qmiles. You can upgrade from Economy to Business Class and Business to First Class. In cases where Business Class does not operate on the flight, you can upgrade from Economy to First Class.
Platinum and Gold members can also redeem their Qcredits for award upgrades.
Tickets issued under certain promotional fares may not be eligible for an upgrade using Qmiles/Qcredits. Please check your ticket or contact any Qatar Airways office for details