I agree with Oreana, new sheets make everything work better. Sum, that line looks worn out, it's not too expensive to replace the sheets and halyards, especially if you learn to splice the eyes yourself. New line feels better to the hand, works better in any type of cleat, and you can get different colors for each line, important for inexperienced crew. I used solid color lines for everything but halyards, you don't want those released by accident, and it's far easier for a novice to "pull on the green line" than to "Harden up the main sheet" and better than "No, not that one!!!"
I would recommend Sta-Set, from New England Ropes, that's what I have, and am happy with it, I have Sta-Set X for the main halyard, but that's overkill, and not as easy to use, Samson makes good line, the stuff at Home Depot may look the same, but it's not!! I have 5/16" line for everything but the mainsheet (3/8", cause you handle that one all the time), the jib downhaul (1/8", doesn't need to be any larger), and the spinnaker sheets (1/4", to cut the weight) Tim