I have lightroom 5.7, do I need to pay to upgrade to lightroom 6? If so, how much?
Yes, you'd have to pay
Lightroom 6 is 79 US Dollars (or approximately the same amount in other countries); OR
you could also use Lightroom CC 2015 which is $9.99/month
Either you can go for a Creative Cloud subscription for 9.99$ a month for both Lightroom and Photoshop or for an upgrade to the stand alone version which would cost you 79$.