If it is a paper pieced pattern that finishes at 6 1/2", you should get 8" by printing at 123% (if it has 1/4" outside seam markings on the pp sections, these would need to be cut at 1/4" as the enlargement would make them too big). If it is a 6" finished pp pattern that is shown with 1/4" outside seams, enlarge it by printing at 133% (same as above on reducing the seam to actual 1/4" on the enlarged pattern).
If it is a pattern that creates a regularly pieced block with an unfinished size of 7" (6 1/2" finished) or a 6 1/2" unfinished (6" finished) and you need to refigure each section; that will take more calculating.