Very carefully suck it out and take out all the dead and floating plant pieces. Stir up the water with your clean hand and start sucking. Since I found this item, I really find it A LOT EASIER doing it this way or you can make one up yourself. No mess or buckets. Easy as pie! You'll see. http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=3910
Try putting a bowl or a tea cup down and let the water pour into that if you can fit it in there. Turn the water pressue on the faucet down a little to slowly fill the tank.
I was reading on another forum, this man in Serbia has a 2.5 x 1 inch ultra-nano tank and he changes the water everyday with a 5 ml syringe. You could always do that.....LOL!! This tiny little tank was unbelievably gorgeous.