how to upgrade icloud storage plan with 10.6.8?

You can only do this from a Mac running 10.7.5 or above, or Mountain Lion; or an iOS5 or above device; or the iCloud Control Panel on a compliant version of Windows.

If you only have access to the Mac and don't want to upgrade the system you could go to an Apple Store and ask the 'Genius' to do it for you (make an apppointment). Note that you won't be able to cancel the automatic renewal yourself .

If you decide to upgrade your Mac you will need to check that it meets the requirements.

The requirements for Lion are:

• Mac computer with an Intel Core 2 Duo, Core i3, Core i5, Core i7, or Xeon processor
• 2GB of memory
• OS X v10.6.6 or later (v10.6.8 recommended)
• 7GB of available space

To purchase it you will have to ring Apple at the number given at the bottom left of this page.

The requirements for Mountain Lion are:

• OS X v10.6.8 or later
• 2GB of memory
• 8GB of available space

and the supported models are:

• iMac (Mid 2007 or newer)
• MacBook (Late 2008 Aluminum, or Early 2009 or newer)
• MacBook Pro (Mid/Late 2007 or newer)
• Xserve (Early 2009)
• MacBook Air (Late 2008 or newer)
• Mac mini (Early 2009 or newer)
• Mac Pro (Early 2008 or newer)

It is available from the Mac App Store (in Applications).

You should be aware that PPC programs (such as AppleWorks) will not run on Lion or above; and some other applications may not be compatible - there is a useful compatibility checklist at http://roaringapps.com/apps:table

We went to the Apple store in Old Orchard (near Chicago). The "friendly genius" allowed me to log in to my account but would not allow the immediate purchase of the additional iCloud storage. She said that I would have to bring my iMac for a Lion upgrade, after I explained that I preferred 10.6.8 as it is very stable and compatible with all my PPC software. It all changes my perspective about the last 28 years of many, many apples computers.