There is more than one casio metal watch band. I was hoping someone would answer this to help me also. Since there was no answer, I gave it a go and was able to do it.
My watch is an e-data bank data memory 350.
There are several "adjustment" segments at both ends of the band. Each one has a sliding, removable piece with an arrow in the middle and a hole and a bump at one end. You need a tiny screwdriver or something with a strong, tiny, blunt end. Hold the watch firmly and carefully and push the screwdriver tip into the hole at a slight angle away from the bump, then, keep pushing while you try to angle the screwdriver tip towards the bump, like you're trying to get some leverage. You may have to try several times. Be careful not to stick yourself. Make some space for this work so you don't lose any pieces like I did.
Once the sliding adjustment piece moves up, you can push the bottom edge until it goes all the way out. Then pull back the segments toward each other on the inside of the band until you can unhook the clasp (the metal piece holding the segments together) from one section.
You will remove a slider, unhook the segment and remove the segment at least twice. I had to do it four times. Keep checking for fit. After the last time, you'll need to take off a clasp on one end and hook the other end with the clasp to that end, then replace the sliding piece to put it together.
You can do some fine adjustment on the end of the band with the spring pin that is in one of four sets of holes. It works to have a sharp knife to poke the end of the pin out of the hole, then reposition the pin to the holes for the best fit and push with your knife tip on the end of the pin to get it back in the holes.
I'm not a jeweler, so they might have a good tool and a better way, but that's how I did it.
Mark Tereau, May 2008