In the event you delete it first you won't have access to a working system
should you run into trouble installing Trisquel. I would at a minimum verify
that you can access the Internet, that there is audio, and your video
displays OK (the screen looks right). You may also have issues printing. If
you do not have an HP printer it is particularly important to check this.
If there is something that does not work you may want to order replacement
parts first. Failing to do so may cause you trouble later.
Now if you are using Trisquel for it's primary benefits, libre (freedom) then
it may make little difference as you aren't going to utilise non-free
software should the install fail (and you need to order replacement parts).
If you are in the US/Canada: 1-888-39-THINK(84465). That will solve the
need/desire to use non-free software (Microsoft Windows) to order free
software compatible replacement parts should they be needed. We have people
call from out of North America although I'm not sure how easy it is or if
there is any blocking being done. The number is a toll-free number in the
US/Canada and non-us customers may not be able to get through without some
manoeuvring.