Just pluck them as far down as you can. the dead leaves should pop off pretty easily.

 

I've found that if you cut the leaves, the cut leaves die eventually, so if you want to trim, you should remove the entire long leaf.

 

Dwarf sag. grows taller as it gets crowded. You might have to thin out the number of plants by pulling them up. It's messy, but it's the right way to do it. It's a water change day project