Unfortunately it is going to cost more money than just buying the Motherboard. You probably will also need to purchase compatible RAM Memory for the 5000 Series APU (Cezanne) processor.
but first try with the RAM you now have for your old APU Processor and see if it boots up with the new Motherboard. If it doesn't then you will know you will need to purchase new compatible RAM.
Look at your Motherboard's QVL List for RAM MEMORY for the 5000 Series or Cezanne processors before buying RAM. Of if the RAM you want is not listed go to the RAM Manufacturer site and use their RAM Memory Compatible Calculator to determine if it is compatible with your Motherboard and Processor.