There are 2 ways to do it.
The easy way that might not work depending on how far gone the structural seams are . Nothing like a 220 gallon flood in the middle of the night.
Here are 2 videos on how to do that.
The proper way would be to cut it apart at the seams with a wire so you have 5 pieces of glass and rebuild it from scratch.
It would be a great project if you like that sort of thing. Kinda like working on an old car. When I was younger, it was an easy way to get free tanks. Now, Im old and have other things to do in my next 75 years of life. For me no. For you ???????
I bought a couple 7ft. long 210's off Craigslist. Stripped them down, resealed and framed them. Its a lot of work, especially removing all the old silicone. If you have the space and time I say go for it.