Question

Which happens to the magnetic field of a wire when you change the direction of the current in the wire?

Answer 1

Nothing will happen to the magnetic field.
BUT If you're talking about the magnetic force , then when changing the current direction , the direction of the magnetic force will be reversed.

(You'ld like to know :
-Changing direction of current ONLY , reverses the direction of magnetic force.
-Changing direction of Magnetic field only (poles of magnet) , reverses the direction of magnetic force.
-Changing the direction of both , magnetic field and current , doesn't effect direction of magnetic force.)

N.B : Magnetic Force is experienced only when direction of current is PARALLEL to direction of magnetic field .

--> Flemming Left Hand Rule is used to know direction of magnetic force.

Hope This Helps.

Answer 2

Magnetic field due to along straight wire is given by the formula

$B = \frac{\mu_0 i}{2\pi r}$

here we know that

r = distance of the point from the wire

i = current in the wire

so here we also know that direction of magnetic field due to current carrying wire is given by using right hand thumb rule as per this rule if we put our thumb in the direction of current then curl of our fingers will show the direction of magnetic field around the wire

So here if we change the direction of current in the wire then the magnetic field direction will also get reversed while the magnitude will remain unchanged