I usually just do a 50% partial once a week on my two 10 gallons. I have one divided 10g, so I usually cup one of the fish, take out the divider, change the water & condition, stick the divider back in, acclimate & free the cupped fish.
Usually I take one of my 1g containers, get as much water as I can into it [1 gallon xD], and pour it in my sink or bathtub. Then once the water level looks about halfway, I take the thermometer and run it under my sink until the temperature looks good at around 76-78 F. Then I put my container under until it's full, then I pour it in the tank [my hand over the water so it doesn't go in all at once]. I keep filling the container up and putting it in the water. Note-I didn't put when I use water conditioner because I use well water which doesn't contain chlorine and all that. But if you're on anything other than that, you should add water conditioner.
Then I put the thermometer back in to confirm the temperature [if it's too cold I just let the heater do it's thing]. Then of course put the divider and fish back in.
But like Dakieda you can use a siphon c: