Need to write to external drive(ntfs) in Yosemite

I have a 1tb seagate hdd that i use to share content between my various PC's which are both windows and mac.

The drive is formatted NTFS, and works fine on all my windows pc's, but for some reason I have read only access when i plug it into my macbook, which is running Yosemite. I have only just noticed the issue because I most often use a flash drive on to move files from the mac to other devices.

I need full access from all my various pc's , as i have some bigger files that i would like to move from mac to windows, and I am also trying to set up a single portable iTunes library, that i can share between all my computers.

I have tried the normal options to change the permissions on the Mac, but it won't let me.

Please assist if possible... there must be a way that i can get full access to my drive without having to format it??