Help with timemachine

[Bulldog VII]

Hi all

I have used time machine for many months with no problems, but today it keep failing to back up & I get a message saying

Time Machine Error

The backup volume is read only

To select a different volume, open system preferences & choose time machine

The only problem is I don't know what I'm doing when I open the system preferences

Can anyone help please

Thanks

 

[Batt]

Click "change disk" and select your backup drive (even though it's the same one you've been using).

 

[Bulldog VII]

Thanks very much all working again now