By default iTunes only takes 1 backup per device. There is no configuration in iTunes at the moment to configure multiple backups for the same device which can cause an inconvenience.
Here is how to create multiple backups for your iOS device in iTunes this works for every device
Step 1: Locate the Backup Folder
For windows this is located in C:\Users\(username)\AppData\Roaming\Apple Computer\MobileSync\Backup
There will be a bunch of files with random names in them. The ones that are date stamped at the end in the formay yyyymmdd are backups that iTunes created when you did some kind of upgrade of your iOS device.
Step 2: Make a copy of the backup folder
Copy whichever folder is the last backup for your device (easily done by checking in windows explorer for the last modified data). If you still cant tell which one it is go into the Info.plist file and check what backup it is there (more on that later)
Rename the folder to something more descriptive and put a date on it so you know when you created it
Step 3: Edit the Info.plist file so iTunes will be able to tell you which backup is which
Open the Info.plist file located in the backup folder you just copied. Locate the string tag just below the key tag for Display Name and edit it to your chosing.
Change the following:
To something that looks like this:
Step 4: Save the file
Now you can restore from multiple backups in iTunes and your backups will be named descriptively.