If looking at changing the look of your retaining wall there are a few tips and tricks you can look at:

Making a blueboard facade is really simple and easy, and can cahnge the look of your wall drastically.

Buy some blue board from your local hardware store like "Bunnings". You can buy sheets in a variety of sizes and thicknesses to suit your application. Make sure you take some measurements to help on wasted material and cut-offs. Using a strong construction adhesive like liquid nails

Buys timber clouts of about 40 mm long to fix into your timber sleeper retaining wall

Try to avoid using screws as they need to be counter sunk to finish flush.

Once you have completed the boarding of the retaining wall it's time to apply a finish to your blue board facade retaining wall.

Either you can use a render with a texture finish or u can use a Sand cement Mortar finish. There are many colors available to the render application.

You can put color into the mix prior to the application or you can put it on afterwards as a paint or a second coat texture finish

Make sure prior to doing works on your retaining wall that the Materials are in reasonable condition to work with. Any rotten or water sodden sections will need to be repaired/replaced prior to work commencing.

Also if your retaining wall is not straight, you should try to even it out by applying padding material behind the blue board.