Hi @katherinechan,
Welcome to the Bunnings Workshop community, it is fantastic to have you with us.
My colleague @EricL has given some comprehensive advice on this topic before. You can check it out here - How to paint skirting boards?
If you can identify the type of paint, oil or water-based, following Eric's advice, then there would be no need to sand it all off. A light preparatory sanding, such as that you've already done, would suffice.
You would then just need to use the correct type of primer, followed by the correct type of paint.
If it is oil-based, use Dulux 1Step Oil Based Primer Sealer And Undercoat and Dulux Super Enamel in a gloss and colour of your choosing. If it is water-based, use Dulux 1Step Prep Primer, Sealer & Undercoat and Dulux Aquanamel in a colour and gloss of your choice.
Enamel paint is best for skirting boards because it dries hard, glossy, and durable, resisting scuffs and knocks, while latex wall paint is easier to apply, dries faster, and gives a softer finish suited to large surfaces. Although the same paint can be used for both, wall paint on skirting will chip more easily, and enamel on walls can look too glossy and highlight flaws. The ideal choice is acrylic wall paint for walls and semi-gloss or gloss enamel for skirting, giving durability, easy cleaning, and a sharp, clean contrast.
If you'd like to paint your walls as well, I'd recommend Dulux Wash&Wear in a colour and gloss level of your choosing.
Let me know what you think and if you have further questions, please don't hesitate to ask.
Jacob
