Hello Irish. Have a go with a sharp wood chisel 
No, really, go real slow at it and any marks you make are under the new spoiler.
Fix your new spoiler with stixall from your local plastics company, you won't need to bolt it, it won't move mate......trust me it is the best.
As well as being a top adhesive, it remains supple enough to run a wire under at a later date if you want to transfer it to another micra.
