I'm not familiar with Alenco, but most of the aluminum windows I've installed you undo the screws at each corner and carefully disassemble the sash frame to get the glass out.
If that does not apply to this window, then there may be snap-in glazing strips around either the inside or outside of the sash that pry off to gain access to the glass.
If you could post pictures of the inside and outside of the sash I could give you a for-sure answer.
An even better idea would be to take the broken sash to a local Glass & Mirror shop. Let them do the work and you eliminate the chance of getting seriously cut. You'd be surprised how fast they'll get it done and for not much money.