Here's what I did.
(1) Filled a bucket with tank water, and removed plants/bog wood, cocnut caves etc and place them in the bucket.
(2) As I have alot of fish I filled a big plastic bin with most of the tank water and put the filter in it, still switched on. Then caught all the fish and put them in the bin.
(3) Nwxt I got rid of the gravel and poured it into another bucket to store. And gave the tank a quick clean and chucked the sand in (which had previously been washed before the emptying of the tank).
(4) Then started adding all the wood etc when tank was back in its position and filling it up again. Part fresh dechlorinated water and some tank water. Then the plants, filter, fish etc.
For me it took a good few hours of my time and you should plan it well in advance. And yeh the water is cloudy after the addition of sand but if you pour/siphon it in gently it will be fine for fish.