Impulse Response to Frequency Response in Octave
The Frequency Response of a system is the Fourier Transform of the Impulse Response of the system.

Since we're in the real world and we have finite number of samples observed over finite time interval we use the Discrete Fourier Transform (DFT).
In Ocatve and MATLAB the DFT is implemented in efficient way using the Fast Fourier Transform (FFT).

In order to calculate it on MATLAB / Octave you can do the following:

% Assuming Impulse Response is given by 'vImpulseResponse'

vFreqResponse = fft(vImpulseResponse);

figure();
plot(abs(vFreqResponse));


Enjoy.