Welcome to forum!
first picture: cut only dried part of flower stem, i would leave half an inch of dried part since i think on the border there is new spike forms.
second picture: all spikes are dried so you can cut it off next to the base of the plant.
third picture: when do you water you plant? Morning, afternoon or in the evening? Looks like maybe in evening? I think those brownish spots appears if you water in the evening. If thats the case change your watering schedule to the mornings. About lower more affected leaf i would caut it off and treat cut area with cinnamon powder.