Read the following warnings, and take them into consideration before you un-install

Don't put your store into Maintenance mode unless you know the ramifications. We suggest unticking the "Put store on the maintenance mode while installing/upgrading/backup creation" as this can lead to problems with Magento's (un)installation functionality having issues and your store entering maintenance mode.

Make sure that Magento compilation is disabled before uninstalling Codisto. After uninstallation, you may re-enable compilation. You can access the compilation options via System -> Tools -> Compilation.

For more information regarding Magento Compilation please see   here under the heading "Magento Compilation / Cache Problems"

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If you installed using the Magento Connect Manager

Open the Magento Connect Manager by clicking the menu System -> Magento Connect -> Magento Connect Manager

Locate the section in the Magento Connect Manager that is labeled "Manage Existing Extensions".

 Find the codisto entry, click the drop-down selection box and select uninstall.

Now click commit changes.

Click Return to Admin at the top. 

You will now see that the eBay | Codisto menu has been removed and the extension is no longer installed.

Please see the  related article to revoke eBay Authorizations

If you installed via FTP

• Remove the Codisto_Sync.xml file from <Magento_Base_Dir>/app/etc/modules
• Remove the Codisto directory from <Magento_Base_Dir>/app/code/community
• Optionally, remove templates from <Magento_Base_Dir>/app/design/ebay
• Clear the cache - remove files from <Magento_Base_Dir>/var/cache

Please see the  related article to revoke eBay Authorizations