Yes, you will have to remove the tank to get at the other spark plug. Make sure you first put the fuel petcock in the "off" (horizontal) position to stop fuel flow. When you lift the tank at bit, you'll need to disconnect the fuel line from the petcock before you can lift it completely off. The line likely will have a spring clip of some kind holding the rubber fuel line tight on the metal part of the petcock. Push that off before trying to wiggle the fuel line off - may need to use a flat blade screwdriver to lever the line off. Good luck with it - once you've done it once it will seem easy enough.
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-Jim
'93 MC21