If you do not have some soldering experience and have not installed or replaced pickups or electronics before, we advise you to have a good technician do it for you. If possible, watch and learn from what you see. If not, look closely at the work after it is done. There is a lot of material on this site that should prove helpful to you if you want to understand and learn more about this.
Replacing the old pickup with one of the same shape and screw hole pattern is simple and straightforward unless the screws do not drive easily into the wood and/or have badly damaged heads. Look and test for this possibility and let the music store where you purchased our product know. They should be able to help you find/buy new screws. Then, put a small amount of paste wax in the screw hole before putting the screw back in. It is a good idea at this point to clean the pickup cavity thoroughly. Stray pieces of shielding braid or steel wool can make problems later (fortunately very few people use steel wool as part of the finishing process now).
Make sure that the pickup can be lowered at least 1/4" or 6mm below the underside of the string. Sometimes the output cable, the output pins or just the depth of the pickup can keep this from happening. If there is metal or paint shielding in the pickup cavity, make sure that it is covered with something that will prevent the pickup output pins from touching the shielding.
If there is shielding in the pickup cavity you should also check that the shielding is properly grounded with a Volt/Ohm meter. From the shielding in the pickup cavity to the ground lug of the output jack, you should measure at worst (in the case of some shielding paints) 20 ohms or so. Good metal shielding will read well below 1 ohm. If you get high meter readings with metal shielding, the grounding wire is not properly attached.
For information on pickup tilt and possible effect on tone and output from the pickup please look at the FAQ: What do I need to about mounting pickups?
Wiring the pickup into existing passive controls: You will find some typical passive wirings here.
Thinking about installing active electronics?
If you do not have experience soldering and wiring electronics. We advise you very strongly to let a qualified person do it - Custom Installations and Repair Shops. The cost of having someone else do it is small compared to the time spent attempting and maybe failing the installation on your own.
If you want to learn about electronics and about installing electronics in musical instruments, you will find some useful material in the basic electronics section of this site. We also encourage you to look into instructional books and videos on this subject. Please remember that we have very limited time for direct support and cannot teach basic electronics over the phone.
If you have experience soldering and wiring electronics and feel confident you can be successful here is more information you can use.