If you see mould, treat it straight away. You can use a specialist mould and mildew product available from a DIY store or supermarket (always follow the instructions carefully). Dry clean delicate items and shampoo carpets.
You can redecorate using a specialist anti-mould paint containing a fungicide to stop the mould coming back. However, you still need to control the condensation levels in your home for it to work long-term. Don’t paint or wallpaper over it.