Can't add/remove files from my Seagate Backup Plus Drive anymore

I bought two Seagate Backup Plus Drives to save all my photos and files. They worked perfectly fine with my MacBook Air; however, about a month ago I bought a new laptop, a MacBook Pro. Now, I can't add or remove any files on my external hard drives. I tried going into the "Sharing & Permissions" tab to give myself access to 'Read & Write' but I get a message saying "The operation can’t be completed because you don't have the necessary permission." It shows the name I had for my last computer, but not the current name of my MacBook Pro. In the 'Get Info' the format says: Windows NT File System (NTFS). How can I resolve this issue without reformatting and erasing all the data on my external hard drives because all my photos and documents are trapped on these external drives. Thanks for your help!