you can go to pet smart or another pet store and get a fish tank vacume and a bucket. take your fish out of the tank and vacume all the water out of it. if you have gravel, plants, or statues make sure to get under them. move around the gravel with the vacume and that should get most of the dirt out. put in new water. it can be from the tap but you need to put water conditioner. you can also get that at pet smart.
Clean filter
Yes it should be OK. I would advocate that you use a filter too and do at least a 50% water change weekly.
Provided the tank has sufficient water (1 inch of fish needs a minimum of 1 gallon of water) and a cycled filter and a heater set to 75F and you change at least 50% ot the water very week there should not be any major problems.
u can use a aqueon 55 gallon filter
No you do not need it because crawfish are not good swimers and can die if you have that much water.
Change 10% of your water (so 1 gallon of water if you have a 10 gallon tank) per week. Change at least 25% of your water monthly.
This depends on the strength of the filtration system on the tank. On a 'normal' five gallon tank (filter turnover about 5x/hour) three or four would be a good number. On a 'five gallon tank on steroids' (I have one of these - filter turnover 12x/hour) I kept seven with no problems. If you're going to keep more than three or four, regardless of your filtration, you need to be religious about tank maintenance - 50% water change, every week. Keeping more than 6 or 7 in the tank is probably not going to work. (For filter turnover, 5x/hour means the filter pumps 5 times the tank's volume each hour, so that would be a 25gph filter in a 5 gal tank.)
It never hurts to have a filter it will only improve your fish's chances of survival and decrease your need to clean.
Bettas and other Anabantids like old water. I would be replacing only around half a gallon (4 pints) of its water weekly.
Freshwater setup: MUST HAVE: Tank, filter, filter pads/media, heater, light, fish, water, electricity, fish food, place to put tank NICE TO HAVE: Substrate, decorations, tank lid
I assume you are asking how to change the water in the tank. Provided you have a filter running permanently there should be no need to change all the water. All you need to do is use a syphon hose and syphon the rubbish off the bottom of the tank into a bucket and keep syphoning until you have removed half the water. Then you simply tip the dirty water into the garden, down the sink or into the toilet and then refill the bucket with sufficient fresh water to which you have added some water conditioner to remove the chlorine,. Then adjust the temperature to match what is in the tank, and syphon the water from the bucket back into the tank. You should only need to replace about 50% of the water each week if you have a properly cycled filter and don't overstock the tank.
It never hurts to have a filter it will only improve your fish's chances of survival and decrease your need to clean.