I keep losing fish and i want to start new and clean the tank all out is that safe

Ive had my tank for over 2 years now and lately i've been losing a lot of fish but ive been losing them right from the start,so i want to clean the tank all out and start from scratch again

First of all, how many gallons is it?

When starting from scratch, I recommmend the following:

If it is fish needing warmed water, heater--> Visi-Therm Deluxe

Filter: Hagen AquaClear

If you still have fish remaining, and you wish to keep it, put it in a tub, like rubbermaid or something, and TREAT THE WATER first, with something like "Stress Coat" or other tap water treatment. If the fish need warmed water, make sure the water is the right temperature. Put the fish in. I would work fast to reduce the amount of time the fish is in the tub.

Empty the tank with a siphon. DO NOT pick up the tank when there is water in it. It could possibly do damage to the tank.

After that, take out all the gravel and wash it out a few times. If there are any decorations, wash those out. If you wish to keep the existing filter/heater/airstone, wash those out.

Set everything back. Add water to the tank and fill it all the way up. Start the filter. Don't turn on the heater at this time. Add some tap water treatment and some stress zyhme or other bacteria booster. Also, treat the water for pH. Put a few flakes of fish food in it (NOT A LOT, only a few) to help boost the bacteria for it to feed on something.

Make sure the fish in the tub recieve oxygen. place any aerating device (airstone) in the tub. Wait 3 days.( I recommend 3 days, general rule of thumb is at least 24 hours. you can split down the processes ahead by what you think.) During the 2nd day in your wait, plug in the heater, and test the water. Adjust pH if necessary. The third day, test the water again. If the pH is stable, put the fish in. When feeding them, feed them only as much they will eat in TWO minutes. Most fish foods say 3-5 minutes, but I say 2, based on my experience.