to edit the model, go to tools>half life>decompile HL mdl
and choose your mdl file you want to work with, then import xxx.smd (xxx being the name of the mdl you decompiled) then go to select in the menu on the right hand side of the screen, click on vertex (right under where you clicked on select) and make a box over the vertecies you want to move, then click on move in the same menu where you clicked on select, THEN move the verticies to your hearts content