A user's internet speed is slow.

Changing the router's password (particularly the Wi-Fi password) prevents unauthorized users from reconnecting to the network. It’s the most immediate and effective response.

“One of the most effective ways to secure a wireless network is by changing the default and existing passwords to prevent unauthorized access.” — CompTIA ITF+ Security Topics

Calling support may help but doesn’t address the issue directly.

Decreasing signal range may reduce but not eliminate access.

Resetting the router is more disruptive and unnecessary if the password can be changed.

Correct answer: C