I have an image which 256x256 pixels in size and i need it to be a 24Bit colour PNG. But the programme won't allow me to do it. Please can anyone tell me where im going wrong or what ive missed. I have photoshop CS4 extended.
An 8-bit RGB PNG gives you a 24-bit image (8 bits per each one of the three R,G,B channels). Is that what you are being asked for?
If so, just make sure your image file is in 8-bit color depth mode.
Did you use Save for Web?