Just use a bucket of soapy water and be careful where you get the water .
You need to keep it away from the wheel axles ,the pedals and the bottom bracket (the axle that holds the cranks and pedals).
Just get a cloth a little wet and wipe all the muck off the frame and any bits which don't move.
Make sure you dry it all well.
If your chain and gears need a clean you can scrub them with some light oil and an old toothbrush.