You need to find the name and location of the file, this can be done by
going to File > Data File Management and going into the Properties of the
file, make a note of this. Close Outlook and then launch Windows Explorer go
to Tools > Folder Options > View Menu > check "Show hidden files and
Folders" > OK press F5 > navigate to the folder where the pst is stored and
move it to your desired location. Open Outlook and it will complain and
offer a browse to dialogue > point it to the new location