I assume that to replace the external micro sd card with a 32 gb one, I need to copy all the files from my current one on to the new one. Is there any trick to doing this or can I just copy everything over using windows file manager?
No trick, just copy them over using any file manager. Copy everything from the old one to your PC, when you install the new one it should format automatically (I think), then connect up to your PC and copy the files from old to new. easy peasy.