I have Installed Windows 7 on an external drive and I want to replace this drive with a larger capacity one. What should I do?
Boot Camp officially only supports installation of Windows onto an internal drive, and isn't required for any installation of Windows onto a dedicated drive. BC's main function is to create a hybrid partition table that will allow both GPT (for Mac) and MBR (for Windows) to coexist on the same drive, and this is Winclone's speciality.

However, if Windows has been installed on its own dedicated drive it will most likely be formatted as NTFS on an MBR partition table. This means you're not restricted to using Winclone and you should be able to use various Windows disk cloning utilities, including Acronis True Image (shipped free with Crucial SSDs, works well). Clonezilla is another package to try, it's open source and free, OS-independent and boots from USB.