Change Multisite setup from Subdomain to Subdirectory

I have just had a site setup with with all the bells and whistles, however it is setup with new sites being subdomain and I want to change this to subdirectory (as I require the theme, menu, etc of the user sites to remain consistent with the main site).

How can I get this changed, or do I have to setup everything from scratch again (even though I paid to have it setup and installed anyway)?

Thanks to anyone who may be able to help.