Q: Upgrading iCloud storage?

You don't have iCloud. You must be running 10.7.2 or later to have iCloud. Mobile Me was terminated several years ago.

Upgrading from Snow Leopard to Lion or Mavericks

To upgrade to Mavericks you must have Snow Leopard 10.6.8, Lion, or Mountain Lion installed. Purchase and download Mavericks (Free) from the App Store. Sign in using your Apple ID. The file is quite large, over 5 GBs, so allow some time to download. It would be preferable to use Ethernet because it is nearly four times faster than wireless.

     OS X Mavericks- System Requirements

       Macs that can be upgraded to OS X Mavericks

         1. iMac (Mid 2007 or newer) — Model Identifier 7,1 or later

         2. MacBook (Late 2008 Aluminum, or Early 2009 or newer) —

             Model Identifier 5,1 or later

         3. MacBook Pro (Mid/Late 2007 or newer) — Model Identifier 3,1 or later

         4. MacBook Air (Late 2008 or newer) — Model Identifier 2,1 or later

         5. Mac mini (Early 2009 or newer) — Model Identifier 3,1 or later

         6. Mac Pro (Early 2008 or newer) — Model Identifier 3,1 or later

         7. Xserve (Early 2009) — Model Identifier 3,1 or later

To find the model identifier open System Profiler in the Utilities folder. It's displayed in the panel on the right.

Are my applications compatible?

         See App Compatibility Table — RoaringApps.

Upgrading to Lion

If your computer does not meet the requirements to install Mavericks, it may still meet the requirements to install Lion.

You can purchase Lion at the Online Apple Store. The cost is $19.99 (as it was before) plus tax.  It's a download. You will get an email containing a redemption code that you then use at the Mac App Store to download Lion. Save a copy of that installer to your Downloads folder because the installer deletes itself at the end of the installation.

     Lion System Requirements

       1. Mac computer with an Intel Core 2 Duo, Core i3, Core i5, Core i7,

           or Xeon processor

       2. 2GB of memory

       3. OS X v10.6.6 or later (v10.6.8 recommended)

       4. 7GB of available space

       5. Some features require an Apple ID; terms apply.

Just to make sure you do know that iCloud storage is only for mobile devices and doesn't backup files from a Mac computer, right?  The following is from this Apple document: iCloud: iCloud storage and backup overview

What iCloud backs up

You have important information on your iPhone, iPad, and iPod touch. iCloud automatically backs up your device over Wi-Fi every day while it’s turned on, locked, and connected to a power source. With your device information backed up in iCloud, you can easily set up a new device or restore information on one you already have.

Here’s what iCloud backs up:

• Purchased history for music, movies, TV shows, apps, and booksYour iCloud backup includes information about the content you have purchased, but not the purchased content itself. When you restore from an iCloud backup, your purchased content is automatically downloaded from the iTunes Store, App Store, or iBooks Store. Automatic downloading is based on iTunes in the Cloud availability by country, and previous purchases may be unavailable if they have been refunded or are no longer available in the store.
• Photos and videos in your Camera Roll
• Device settings
• App data
• Home screen and app organization
• iMessage, text (SMS), and MMS messages
• Ringtones
• Visual Voicemail

So if you're looking for backup for your Mac iCloud is not an option.  Instead get an external HD and use Time Machine which is included with your Mac.

OT