i have a fujitsu laptop with os vista but in a japanese language. how can i change this language to english without changing m

You will have to buy and install a full English version of Windows, (not necessarily Vista, or even Windows 7, because those versions are no longer officially on sale. You might find copies of them from online vendors though, but keep it legal.

You will have to completely wipe the Chinese version off the hard drive before you install the English version.