Hello Gabriel,
Most likely you are using a Categorical axis. You can flip the X axis labels from: Chart Areas >> Axes >> Primary X >> Scale >> Categorical >> First Level
Change the First Level Label Angle to Scale and enter: 45
This can be achieved for a Numeric axis as well.
You can also change the size of the axis labels or uncheck the "Stagger 2" option from: Chart Areas >> Axes >> Primary X >> Advanced
Hopefully this helps.
Best Regards,
Nevron Support Team