if you know about what size they need to be install them first. You can install the after also. after a while rejetting will take about 10 minutes. to answer your question it really doesn't matter your going to be changing them again anyhow
no in the float bowl there should be a large bolt that can be taken out. theat gives you acess to the main jet. if not then you will only need to flip the carb and pull the bowl off. in a perfect world you will learn the sled and know when abouts you need to change or better yet be jetted before you get there. with the float bowl removed it is i think a 3/16 socket that will unthread the jet and a new one will be replaced. it really isn't that bad once you've done it a few times
Not remove the carbs completely but you will have to take them out the boot to turn them upside down at least to access the nut. You don't have to take the throttle cable out though. I believe the standard jet size is 1/4"? Best thing you can buy for changing jets is a standard screwdriver with the interchangeable bits. put the bits in your pack but the screwdriver part should fit the main jet perfectly. I use the Craftsman one and it seems to fit perfect. Keep in mind that they are easy to overtighten, they are only a small brass thread, so don't tighten them too much but tighten them enough that they won't fall out.