Summing up the solution from the comments and expanding:
This process basically includes two steps:
- Create a backup
- Transfer it to the Windows PC wirelessly
A further pre-condition for the following is that the device is rooted, which is the case here.
Create the backup
Depending on what you need to backup, there are different good solutions available (you can see the backup tag-wiki for more information):
All three options store their backups on the SDCard. So if your device features a microSD slot, you could even simply take out the card, and attach it to your PC using a card reader. This generally works without a cable, and such could also count as "wireless" :)
One thing you might need to care for manually are the media files, and other downloaded/manually created stuff. Usually, this is stored on the SDCard as well – but that could be the internal one, so in case of the "card-reader option" you might need to copy stuff to the external card manually, which can be done with a good file manager such as ES File Explorer.
Transfer via WiFi
Now for the WiFi transfer. This can be done with the just mentioned ES File Explorer, which includes a "Samba client" to access Windows shares: Just share a drive from your computer, and then copy all files over. This also can be done "the other way round", pulling the files: with e.g. Airdroid you can access your device from any web browser. Airdroid includes a file manager, and lets you upload and download files.
Another more elegant variant, especially if you want to automate things, is to use a sync tool. Here you might want to take a look at FolderSync: As the name suggests, this app lets you synchronizes files and folders. Like with ES File Explorer, you can use Samba/CIFS here to access a Windows share.
Elegant permanent solution: Set up scheduled backups with Titanium Backup, and set up a matching sync interval for TiBu's backup directory with FolderSync. That way you always have an up-to-date backup off-board your device, in case of brick/loss/whatever.