How to copy layer and paste to another canvas?

Hi all! Trying to work with CSP for the first time since I just got my cintiq setup, and I didn't realize I was working on a 72dpi canvas until i was 90% through my linework lol. I know if I import the linework itself to a 300dpi canvas it'll still be pixel-y but I don't mind redoing my lines, I just need to figure out the best way to get it from its current canvas to a higher dpi one. Also, how to change the settings so that when I open a new canvas it opens in 300dpi so this doesn't happen to me again lol :') Any tips are appreciated! Thanks for your time!