You just take apart the top and remove the existing fixture and install the new ones. not much electrical has to be done. Wish I had a picture of my old set up.
Sounds silly but I modified my 65 gallon and put in some LED lights with some DIY you can put any light in there. I put 2 vipar spectras for full coverage. It worked for 5 years but you will have to install a fan also.
My 2 go to spots since I live in Queens are Kissena aquarium which I have been going to for over a decade and NY Reef Aquatic. Both are very reasonable and the owners are just top notch when it comes to helping and answering questions.