I had the same difficulties mentioned by others and wanted to upgrade to the latest version of Magento. Here is a collection of info from various sources. I applied the steps and was able to complete the upgrade.

Steps to upgrade Magento ecommerce package on myhosting.com to the current version 1.1.6

1. Backup your database and the .htaccess file found in the root directory of your ecommerce site

2. Backup or copy all the code you modified yourself, and don't forget to keep
the original installation archive

3. Also copy and save the media directory that contains all the uploaded
product/category images

4. Copy the app/etc/local.xml file

5. Download a new installation file -> http://www.magentocommerce.com/download/noregister

6. Extract and upload all the files it contains to your ecommerce directory on the server

7. Delete var/cache and var/session directories

8. Upload the original .htaccess file to the root directory of your ecommerce site

9. Point your browser to any Magento page and let it begin the upgrade (this stage begins creating new tables on your mysql database)

You will probably see the following errors


Error in file:
"/var/www/domains/shop.puravidabooks.com/docs/app/code/core/Mage/Sales/sql/s
ales_setup/mysql4-upgrade-0.9.9-0.9.10.php" - SQLSTATE[HY000]: General
error: 1005 Can't create table './shop_puravida769/#sql-b8b_286da3.frm'
(errno: 150)
Trace:
#0
/var/www/domains/shop.puravidabooks.com/docs/app/code/core/Mage/Core/Model/R
esource/Setup.php(286): Mage::exception('Mage_Core', 'Error in file: ...')
#1
/var/www/domains/shop.puravidabooks.com/docs/app/code/core/Mage/Core/Model/R
esource/Setup.php(178):
Mage_Core_Model_Resource_Setup->_modifyResourceDb('upgrade', '0.8.25',
'0.9.20')
#2
/var/www/domains/shop.puravidabooks.com/docs/app/code/core/Mage/Core/Model/R
esource/Setup.php(145):
Mage_Core_Model_Resource_Setup->_upgradeResourceDb('0.8.25', '0.9.20')
#3
/var/www/domains/shop.puravidabooks.com/docs/app/code/core/Mage/Core/Model/R
esource/Setup.php(120): Mage_Core_Model_Resource_Setup->applyUpdates()
#4
/var/www/domains/shop.puravidabooks.com/docs/app/code/core/Mage/Core/Model/C
onfig.php(215): Mage_Core_Model_Resource_Setup::applyAllUpdates()
#5
/var/www/domains/shop.puravidabooks.com/docs/app/code/core/Mage/Core/Model/A
pp.php(236): Mage_Core_Model_Config->init(Array)
#6 /var/www/domains/shop.puravidabooks.com/docs/app/Mage.php(424):
Mage_Core_Model_App->init('', 'store', Array)
#7 /var/www/domains/shop.puravidabooks.com/docs/app/Mage.php(443):
Mage::app('', 'store', Array)
#8 /var/www/domains/shop.puravidabooks.com/docs/index.php(52): Mage::run()
#9 {main}

If you do, you should be able to solve them by doing the following:

The solution mentioned below was successful (explained in some greater detail here:
http://www.magentocommerce.com/boards/v ... 30/#t62082 ):

ALTER TABLE catalog_product_entity ENGINE=INNODB
ALTER TABLE core_store ENGINE=INNODB
ALTER TABLE eav_attribute ENGINE=INNODB

If customers need to make these updates on their own, via the phpMyAdmin web utility, they can click on each of the three table names listed above, then click on the Operations tab, and change the Table Type to "InnoDB", if it is not set to that type.

These steps, collect after working and communicating with myhosting.com and the team of the myhosting.com forums, worked for me. NOTE THAT YOU WILL HAVE TO UPLOAD OR MANUALLY MODIFY THE VARIOUS PORTIONS OF YOUR SITE WHICH WERE CUSTOMIZED. You may also have to upload the product/category images files for your products (may or may not, as the upload process does not overwrite files if they do not exist in the new package).