Welcome to GeekHack!
Browns have a small tactile bump which I find helps a lot, especially when typing, but some find too small.
Clears have a larger tactile bump and stronger springs. I like Clears and ErgoClears (Clears with lighter springs in) the most. I actually find ErgoClears best for gaming, too, since you can use the bump as a reference point of where the switch actuates and sort of rest it on the upward part of the bump for lightning fast direction changes and double-taps.
Clicky switches have something called "hysteresis" which means the reset point of the switch is above the actuation point so you have to lift your finger quite high when you want to double press the key. Blues are soft spring clicky switches, Greens have harder springs and Whites are like Greens, but with a slightly different slider so the clicky part doesn't hit the casing, but rather the rest of the slider, so they are quieter.
In order to change the switches on the K65 you will need to desolder the old switches from the board, even if you just want to open the switches and change the internals, since the board is plate mounted and the plate doesn't have slots to allow opening the switches. If it's backlit you'll have to also desolder all the LED's.