How to change/calculate frequency of this oscillator circuit?
With a pure RC oscillator, the easiest way to scale the frequency without understanding the circuit is to scale all the capacitor values, or scale all the resistor values. Neglecting strays, the frequency will vary as 1/RC.

This can go wrong, if the resistors get too small to be driven by the opamps, or too big to provide bias currents, or the capacitors get too small to swamp stray capacitance. There's a wide range where they should work, anything in the 1k to 10M range, and any cap above 100pF.

This is a phase shift oscillator. Without studying it too carefully, there appear to be two filter sections that together with any signal inversions provide 360 phase shift at 1kHz. The feedback uses a filament lamp to stabilise the amplitude, though a thermistor would be a lower power alternative for this.