Changing the network address of your computer won't improve wireless signal. Some say changing the wireless channel to one that is less busy can help get a cleaner signal but I've never known of any interference in a band where switching channels could make any difference.
If you really want to set a static network address for your computer you'll need to find the MAC address of your PC and access the router console to assign an IP to that MAC address. Honestly though automatic lease is fine for anything you need.
You're only options are to boost the signal, get the computer closer to the transmitter, or use a wired connection.
If it really is your neighbour's wifi as patio says then you're stuffed unless your neighbour is willing to move the router closer to your adjoining walls.