A positive charge and a negative charge of the same size are each released from rest in a uniform…

Step 1. The directions. The positive charge moves along the field, towards lower potential. The negative charge moves against the field, towards higher potential.

Step 2. The potential energy. Each charge moves the way that lowers its potential energy $qV$. For the positive charge this means a fall in $V$. For the negative charge $q$ is negative, so $qV$ falls when $V$ rises. So the potential energy falls for both.

Step 3. The kinetic energy. Each charge gains kinetic energy equal to the potential energy lost, which is $|q|$ times the size of the potential difference. For charges of the same size and the same potential difference, the gains are equal.