You are a 17 year old girl; I am a 70 year old woman. You are probably stronger than me. I change 88 litres water every week in my main tank using buckets.
I siphon water out of the tank into a builder's bucket 7 times and carry the bucket just above the floor outside to the drain. Then I run 8 litres tap water into another bucket 11 times (putting dechlorinator in the bucket before running the tap), carry it to the tank, lift it onto a tall stool and use a 1 litre jug to ladle the water from the bucket to the tank. The only time I didn't do all this was after cataract surgery and I wasn't allowed to lift buckets of water for a month, so my husband carried the buckets and I just used the siphon and the jug - the surgeon said I was allowed to lift 1 litre.
Compared to that, a 20 litre water change in a 41 litre tank would be so easy.