Change from Gravel to Sand...

As long as you keep your filter media wet while you do the substrate change, you shouldn't totally kill the cycle--only part of the bacteria live in the substrate anyway. Changing water certainly won't kill your cycle.

I've never done it myself, but if I was going to do it, I'd remove all the tank inhabitants (fish and plants alike) and keep them in a bucket of tank water, float the filter media in the bucket with them with an airstone to keep the water moving, then empty the tank and put the sand in, replace ornaments and plants, refill from bucket, add fresh water, and voila. I'd check water parameters daily for a little while 'cause the bacteria in the gravel would be gone so the readings might not be perfect right away, but since the filter media will have been saved, I wouldn't worry about crashing the cycle.

'Course as I said I've never done it, so wait for the experienced replies, heh.

Changed all my tanks a couple months ago from gravel to pool filter sand; took all day but worth it. You only have a 10 gallon, should be a quicker job!

Got some storage tubs and siphoned some of the tank water in them.

Put decor in tubs to save the bio on them.

Plants went into the water.

Filter carts went into tub.

Turned off heaters and filters.

Started draining tank and netting fish out (getting the fish out was easier the lower the water level was!)

Scooped out all the old gravel, left fishie mulm behind-good ferts for the plants.

Scooped in pre-rinsed sand.

Filled tank halfway so heaters were submerged, turned them back on.

Replanted plants, put decor back in.

More water in tank, watching the temp.

Fishies back in the tank.

You could swap out now. Most of the good bio is in the filters and decor, some in the gravel, very little in the water.

Up to you!