Answer
The change in speed is decreasing.
Work Step by Step
The sign of $v_x$ is $~~-~~$ so the object is moving in the $~~-x~~$ direction. The sign of $\sum F_x$ is $~+~$, so the acceleration $a_x$ must also be in the $~+x~$ direction. Since $v_x$ and $a_x$ are in opposite directions, the speed must be decreasing.
