lowpass filter matlab
The command fir1 in matlab implements digital filters based on the window methods , as you indicated the comand h=fir1(n,wn) returns the nth +1 coeficients of a Hamming window lowpass linear filter, the vector h is the coeficients of the filter from wich you will convolve the sample demodulated signal. If you want to use other window than hamming, for instance if you need a attenuation in the stopband higher than 44 db you can use h = fir1(n,Wn,window) where widow should be a colum vector resulted from a desired window see blackman and kaiser in the matlab help.
Dont forget that Wn is the normalised frequency i.e the desired cut off frequency over Sampling frequency.
n is the number of coeficient of the filter, it depends of the transition width ( normalized) and the window used, for a hamming window n=3.3/( transition width). Remember to normalize the transition width related to the sampling frequency and that transition width = stopband - passband
After find h from fir1 you can peform as the pall b.pricope suggested :
FilteredOutput = filter(h,1,DeAmpMod);
where DeAmpMod is the Demodulated AM modulated signal you want to filter.
I hope have helped