Won’t find OS X partition

Hi all, Gavin issues with my Mac, can’t remember what version of OS X it was running, either Mavericks or Sierra.

Since I bought my MacBook Pro a couple of years ago I’ve had a 350gb OS X partition, and a 150gb windows 8.1 partition. I found I don’t need anywhere near 150gb on windows side of things so tried to reduce that partition, but it wouldn’t let me do it like the instructions said I could. So I went in to windows and reduce the partition there, leaving an excess. I then shut down to reboot in OS X to allocate the now available space to the OS X partition, but on startup it only gave me the option of booting from windows. I shut down and started up holing the option and R key, and this took me to a screen with a picture of the world and a timer, after about 25 mins I was able to select disk utility, and when I went into it, on the options down the left hand side I have the overall mac HD 500gb, clock that and it then shows the 150gb windows partition, but nothing to select the OS X partition. On the overall display it shows 150gb bootcamp/windows, and 350gb ‘untitled’.

Has anyone got any ideas of how to get it to ‘see’ the OS X partition, or any suggestions of how I could try and backup all my photos and music etc, and then wipe the whole drive and revert back to soley OS X on there, as I no longer need windows anyway.

Any help much appreciated, but please try and explain simply as I’m not too sure what I’m doing.

Thanks.