Hello again Hayo, thanks for the response.
Have tried deleting from PM5 contact sheet which seems to work sometimes and not others. On other occasions I have also had error messages saying that I do not have permission to carry out the task. Tried changing permissions but I now suspect that, as you pointed out, it is a permissions issue with the iMac rather than PM5. Have managed to delete an image by a convoluted work around, mainly guesswork, but will be going onto to Apple chat later today to see what they can suggest. Suspect now the problem is my ignorance of the Apple OS having just moved from Windows. Will let you know how I get on.
Kind regards, Frank