How do i drain and change the oil in derbi senda r 50 after waters mixed with the oil?

Answer 1

there is no two answers for that...

it is dangerous for the engine to run with oil mixed with water...

drain and change as soon as possible

Answer 2

I can't tell you all the particulars from the limited amount of pictures of your bike.
-Remove the oil drain bolt on the bottom of the crankcase (the universal bolt size for bikes, use a 17mm wrench).
-Drain the oil (remember to recycle).
-Re-install the drain bolt with a new sealing washer if necessary.
-The oil fill cap should be some where on the top of the crankcase. About 1" or 25mm in diameter with a raised tab for turning.
-Fill with recommended oil.
-There are 2 ways to check oil level on dirt bikes.
1) Oil level check bolt. On the right side cover.
2) Oil level site glass. A 1" round piece of glass on the side of the crankcase. Usually by the kick start & R brake lever.
-Always check the oil level with the bike upright (as if you were sitting on it).
-Check bolt - fill with oil slowly until oil comes out of the check bolt and re-install it.
-Sight glass - fill with oil to cover 3/4 of the sight glass.
-Remember to hold the bike upright when adding oil.