Patience is key here. If it's a rosewood (or similar) fretboard then be VERY careful when removing the frets, as it splinters very easily. Heat them up with a soldering iron to let them lift themselves out of the grooves before carefully pulling them out. Get a radius block too for the smoothing/sanding after the gaps have been filled in - these come in various sizes, so check with a radius gauge first - you might need two, as some boards have a compound radius (slightly different radius closer to the nut than the bridge).