I'm probably mentioning things you already know here but...
The common concerns are dealing with leaking hydraulic fluid all over the place and the possibility of some line being under pressure. Be sure to mark the hoses and ports on the original valve with colorful tape to avoid wrong connections on the new valve. I would first put the machine a place where you can let it sit for a while depending on what goes wrong. Lower the loader to take as much stress off it as you can. Then rock the joystick slowly in all possible directions (which will take pressure off the lines.) Looking at the photos you do not have quick disconnects in the lines. Just take them loose from the loader valve body one at a time, watching to see if you get leaking/running/dripping. Plan ahead by preparing a place (or even some clamps) where the loose ended lines can be kept up at the height of the loader valve -- won't run fluid out so bad as they would if let dangle. Of course you will get a small amount of fluid no matter what you do so a few rags are in order. Hang on to any instructions or diagrams that come with the new valve. Esp see if the papers offer instructions for making adjustments during installation. Typically the only adjustments are "in and out" distances for each of the two control cables and a lock nut on each one when it is correct. However your original valve looks to be the type with the joystick mounted directly on the valve body so there would be no control cables to adjust for penetration. With a little luck your new valve will be adjusted at the factory. Just reconnect all the hoses making sure you get them in the same ports on the valve as the old one. Fire it up and let it run a minute or two to get full hyd pressure. Then try it -- all operations , up down loader frame & curl/dump of the bucket. If those movements all work correctly, you probably do not have to do anything else. Study those papers that come with the valve looking for any less-than-obvious instructions or adjustments. Do not worry about air in the lines, etc. which may cause momentary issues until the cylinders have all been activated full in and full out. They are self-purging of trapped air. Normally not a problem. There are all sorts of fairly rare issues (such as external shims on each of the 2 spools in the valve, etc.) You are unlikely to have those issues. If you do, there are probably adjustments inside the base of the joystick under the rubber boot. Unlikely needed. If the paper directions provided fail to give adequate help, the prominent loader valve manufacturers all have customer service phone numbers you can find on the web or the papers. I've had one mfr (Nimco in Wis.) turn my phone call directly over to an engineer with immediate first-hand familiarity with my valve model. Even though the valves were made in Sweden.
This lengthy discussion makes it seem like a lot bigger job than it is. Good luck and let us know how it works out.
