Yes and No depending on which type of box and the way the cables run into the box most percentage it useally not a major issue however most box useally have two nails expect the steel box that kinda toss up depending on the type of junction box.
To remove the single gang box to two gang box .,
Before you start that make a note of wireing connections first this is very important part otherwise it will be a headache to get it hook up right again after you change the junction box.
Once you mark them down what they are for and how it hook up.
then take a old screwdriver or prybar and pry it to one side most case it will pop off then twist the box it will come out.
To install the new box normally I get what we call Smart Junciton box { not all big box store may stock this } otherwise a old work junction box will work in this useage.
This is a link so it may give you some idea how we use for old work boxes
But not all big box store will stock this item otherwise electrical supply centre will have this.
http://www.arlcatalog.com/Miscellane...et%20Boxes.htm
Merci,Marc