Welcome to the forum. Usually the lens will pop off by using a small flat blade screwdriver on the bottom of the lens. The bulbs are held in by "tension fit" and make contact on a copper finger. Sometimes all you have to do is clean the bug webs or corrosion off to get the lights to work, or else the bulb is burnt out. If none of the marker lights are working, then you probably have a blown 12v fuse. Hope this helps.
2014 FR Heritage Glen 282RK
2013 F250 HD 6.7L Diesel
Formerly Owned: 1995 22D Fun Chaser & 2901L Classic