There’s really only one way to change out a fly, just cut the line and tie on a new fly. Nippers are definitely a good idea, your teeth will appreciate the investment. After you cut off your fly, check how much tippet you have left, most of the time I want to have at least 8 inches of tippet to work with when I’m fishing nymphs or drys.
When to change flies is a much more nebulous topic. Even very experienced fly fishers will struggle to answer this question.
When fishing dries, it can be fairly obvious when to switch flies, when the fish aren’t rising to your fly, swap it out. Fish refusing your dry fly is a sign to change to a slightly different pattern, maybe try an emerger or cripple, or try a different size. If the fish are completely ignoring your dry fly then switch things up more drastically.
It can be really difficult to decide when it’s time to change flies while you’re nymphing. Typically, if the fish haven’t given my flies any attention after 10 - 20 casts in the same spot, I will change things up. Another option is to move to a different location and try some casts there. Either way after getting 15 - 20 good drifts through an area you can be fairly sure that the fish aren’t very excited by your flies. On certain rivers and certain conditions, sometimes this rule doesn’t hold true and the fish are just finicky. When you’re unsure what to do, follow your intuition.
When streamer fishing, changing flies is about confidence and conditions. When you're searching for a trophy trout with streamer tactics, you don’t want to waste your time on the water constantly tying on new flies. Pick a fly you have confidence in and pick a fly that works in the current situation. Fishing in a deep pool on a cloudy day? Tie a black weighted streamer on. Fishing a tailout during brown trout spawn? Throw a big unweighted yellow streamer. Once you have lost all confidence in your streamer choice is when you should swap it up.
As you get more experienced with fly fishing it becomes easier to decide when you need to switch flies. Certain rivers and certain species of fish have their quirks. If you’re having trouble on any of our local lakes or rivers, give us a call or stop in at the shop. We’re always available to provide you with the inside scoop.