Q: imac with  OS X 10.9.5 needs upgrading to sync with my ios 8 devices

Please be much more descriptive. Exactly what in iCloud are you having difficulty with, also have you checked your iCloud settings on your iMac to ensure they sync with what you have input on your iPhone and iPad?

Did you enable the iCloud Drive on your iPhone? 

If you did that's the reason you can't sync between your Mac and devices.

WARNING:  If you use iTunes to sync photos between your iPhone or iPad and your Mac do not activate the iCloud Drive. Doing so will kill the capability of using iTunes to sync with your mobile device and disable Documents & Data syncing for your iCloud account on OS X Mavericks and earlier Macs, as well as iOS 7 and earlier devices.

If you use iTunes to sync photos between your iPhone or iPad and your Mac do not activate the iCloud Drive. Doing so will kill the capability of using iTunes to sync with your mobile device

What is your source for that information? I see no connection between iTunes and iCloud Drive.

From the OS X Yosemite Developer Preview 8 Release Notes which states:

iCloud Drive

Note

Migrating to iCloud Drive will disable Documents & Data syncing for your iCloud account on OS X Mavericks and earlier Macs, as well as iOS 7 and earlier devices

There's nothing in that document about iTunes. iTunes has no interaction at all with iCloud in any version of OS X.

You're right. It's not mentioned there.  There are two issues here, document syncing and photo syncing.  The syncing between the iPhone and iMac of photos vis iTunes is affected it seems.  User léonie has tested it and reported in one of the topics. I'll be more precise in using that warning next time.  Am trying to search for it currently.  The iCloud Drive has messed up a number of features we once enjoyed.

Link, I think, Old Toad remembered my warning here, that I posted in the iPhoto forum:

A Warning: Syncing Photos with iTunes to iOS 8 Devices

After upgrading to iOS 8 and enabling both iCloud Drive and iCloud Photo Library (Beta) I noticed, that iTunes Photo Sync was no longer available in  iTunes with  MacOS  X 10.9.5 or later.

iTunes would not offer to sync photos with the message: "iCloud Photos On:  device .... can access photos in iCloud. Photos can be downloaded to your device via Wi-Fi or cellular network".

The fatal setting in this case is enabling  "iCloud Photo Library (Beta)". It lets you sync between mobile devices, but since there is not yet a corresponding Photos.app for MacOS X, we still need iTunes Photo sync to sync the Photo Libraries to the mobile devices. Fortunately, disabling "iCloud Photo Library (Beta)"on the mobile devices brings the capability to sync photos with iTunes back.

imac with  OS X 10.9.5 needs upgrading to sync with my ios 8 devices

I cannot use icloud now with my iphone and ipad that upgraded to IOS 8.02. When I try and get the imac to upgrade, it shows none are available. HELP

Jill, you are running already the last OS X 10.9 version of MacOS X and cannot update beyond that using software update from the AppStore. Only Beta versions for Yosemite are available to upgrade beyond your version. Wait till the end of the month, when the new MacOS X version will probably be released.

See this document on using iCloud with iOS 8:  iCloud Drive FAQ