When looking at the velocity magnitude plot, how do I get rid of the grid?

RTFM

R u sure? Do i enter this in the es-aero output window? Because I do and it says unrecognized command

You switch the mesh off and on by plmesh,off (on). There are buttons along the left side the of the plot window that also turn it on and off and there are more buttons in the post-processing section of the navigator to allow you to customize the plot. You might also try the edge command.