Matlab signal processing removing white noise from signal
Without further details on the signal and the type of processing you want to apply, the two most basic approaches are:


signal enhancement via linear filtering (filter or filtfilt),
Wiener filtering, assuming a known stationary signal and noise spectra in an additive noise (matlab code).


If your signal is non-stationary, a time-frequency (spectrogram) or time-scale (wavelet) decompositions might help. In their domain, signal and noise are often better separated, and you can there apply Wiener filering, or alternative forms of thresholding, or more involved source separation techniques.

Wiener filtering in the wavelet domain are generated a lot of works, and codes, that you can test.