Changing template on a live site

[Guest]

Hello all,

 

I've got a live osC site at the moment and I want to give the site a revamp with a new template, colour scheme etc etc but I don't want to take the site offline to do this. Does anyone know how I can work on a new design - say for a few weeks whilst the site's still online without anyone noticing any changes on the front end of the site?

 

TIA

 

Sam