That is a walking beam and meant to move. You could get it centered and hope for the best, however, I would suggest going directly under the frame and utilizing jack stands if you are removing all four tires.
If you are only removing one tire at a time, then don't use a jack at all. Drive the tire that is staying on up onto a ramp. This will lift the other tire off the ground.
2015 White Hawk 25BHS Glacier Package
2004 Dodge Ram 2500, 5.7 Hemi, 5Spd Manual
2008 Arctic Cat M1000 SnoPro
Previous: Northface tent/Komfort 5er/Jamboree MH
Lance Cabover/Prowler TT/WildernessTT/Tiltin Hiltin Cabover/Starcraft popup