Shift signal in frequency domain
If you merely want to shift spectral samples up in frequency, the process is fairly simple.  Let's say your DFT comprises the eight complex-valued samples X[0], X[1], X[2], X[3], X[4], X[5], X[6], X[7] and you want to shift them upward in frequency by two samples. The new shifted Y[m] spectral samples would be: 

Y[0] = X[6]

Y[1] = X[7]

Y[2] = X[0]

Y[3] = X[1]

Y[4] = X[2]

Y[5] = X[3]

Y[6] = X[4]

Y[7] = X[5]

You'll notice that the shifting could be described as a "circular shift" because of the sample wrap-around behavior. If you want to shift your original X[m] sequence downward in frequency by three samples. The new shifted Y[m] spectral samples would be: 

Y[0] = X[3]

Y[1] = X[4]

Y[2] = X[5]

Y[3] = X[6]

Y[4] = X[7]

Y[5] = X[0]

Y[6] = X[1]

Y[7] = X[2]