Sat Nav update

Hi all Have just decided that I need a SD card to update sat-nav maps on Karoq although the satnav woks there is no SD card 

I learnt from this forum once down loaded onto SD card and transferred into satnav the SD card can be wiped clean I reckon

that was what happed to my Karoq as there was no SD card when I bought the car the previous owner must of taken card out 

Question what size card will I need and how much does it cost ..... Thank you .... Regards Gary 

                                                                                                                                                                      PS I think the CD player is a Columbus