@josehoward Thanks for reaching out!
In order to determine which size backpack is correct for you, you will need to know a couple of measurements. You can find out how to take those measurements in the Expert Advice article How to Size and Fit a Backpack. The Osprey Talon 44 comes in two sizes, S/M and M/L, and the torso lengths for each of those sizes are listed in the specifications section on the product page. Once you have your torso length measured, you just need to pick the size that best corresponds with your measurement.
Hope this helps!