How does current change in a parallel circuit?
Current splits between the branches.
The current along the branch with the smallest resistance will be larger than the branch with higher resistance. The total current in the circuit must remain constant (so that charge is not created/lost). So the sum of the currents in the parallel branches will always be equal to the current before the junction.
If the resistance in one branch is decreased the current will increase along that branch. In order to compensate for that current increase the current in the other branch must decrease so that the total current will remain constant.