Save Game on Cartridge.

Just wondering, if i have a save game on the actual cartridge (as in, bought the game and have a save stored on it), is it then possible to get that save onto my R4?

Yes. There are various homebrews that will do it for you. You can use the same ones that backup actual games from the cartridge through either WiFi or an EZFlash 3 in 1. Check out http://www.linfoxdomain.com/nintendo/ds/ and look under "Essential Utilities".

Having troubles figuring all this out, i'm not sure the Wifi one will work for me as my router is on WPA2. Are there any tutorials to follow? Haven't been able to find one on this site :(

Yes, there are tutorials.
https://www.romulation.org/forum/index.php?topic=33928.msg607244#msg607244And no, the DS won't work with WPA2, and the programs won't work on the DSi which supports WPA, so you'll have to change your router to WEP.