Hino,
Your book is more likely to give you the answers, as it is a long and complex subject.
What do you mean by Performance? Maximum speed? Maximum range? Jet? Turbo prop? Piston? Turbo Normalised?
In general terms, you have the basic idea- Drag is (simplistically) proportionate to Calibrated Airspeed- as altitude increases, True Airspeed increases as a function of CAS, so all other things being equal speed and range will increase with altitude.
That, however, assumes thrust is constant. As altitude increases, available power reduces, so the point at which maximum performance is available is the highest altitude at which the power required for a particular CAS is available.