Wire on one speaker is loose...can get sound only by jiggling and holding wire just so...can I replace the wire? how? thanks!

Hello, most probably you will not be able to replace the wire so that the speaker system remains as "good-looking" as after buying it. I am also not sure if the company or it's vendors might be able to replace it for reasonable amount of money. Most probably they would advice buying a new one. I think the best way would be for you yourself trying to repair you speakers wire. It most probably got damaged or broken, that's why you still can hear the sound while jigging the wire.
In this case i would advise repairing the wires with soldering iron. you will need to cut out the part of wire which is damaged (most probably aproximately around 5cm of wire) and after you will have to simply strip the 3 wires from their cover, and solder them with the soldering iron. Be cautious to wrap each soldered part separately with a small piece of insulating tape or duct tape in order to prevent them from contacting with each other.

Which speaker? Assuming you mean the external wires, one speaker has as simple twin lead, but the one with the volume controls is much more complex. Off hand if you are asking, you may not have the required skills to make the repair. :(