The IP address is set by your ISP, tampering with it without knowing what it's meant to do, will only give you negative returns. Might be possible that the latter speed test was conducted during a higher traffic period resulting in lower speeds. On another note, you've posted this thread on the wireless section. What are you using to connect wireless to the router? Smartphone? Desktop? Laptop? If a desktop or a laptop, mention the make and model of the wireless adapters. Make sure you're on the latest drivers for them.