1. To achieve this via Workbench, create a folder on your desktop. I will call my folder ‘deleteClasses’.

2. Then go to Notepad (or another text editor) and copy and paste the below and save as the file with ‘package.xml’ and ‘All files (.)’.

   <?xml version="1.0" encoding="UTF-8"?>
   
   <Package xmlns="http://soap.sforce.com/2006/04/metadata">
   
   <version>30.0</version>
   
   </Package>

3. Then create a new file in Notepad (or another text editor) and copy the below into it:

<?xml version="1.0" encoding="utf-8"?>

<Package xmlns="http://soap.sforce.com/2006/04/metadata">

<types>

<members>SomeClass</members>

<name>ApexClass</name>

</types>

<version>30.0</version>

</Package>

<?xml version="1.0" encoding="utf-8"?>

<Package xmlns="http://soap.sforce.com/2006/04/metadata">

<types>

<members>SomeClass</members>

<members>SomeOtherClass</members>

<name>ApexClass</name>

</types>

<version>30.0</version>

</Package>

1. Save this file name as destructiveChanges.xml (note the capital ‘C’ in ‘changes’). Make sure the file is saved as ‘All files (.)’. More information on destructive changes can be found here.

2. Now there are two files in your folder. Open the folder, select both the XML files, right-click and select ‘Send To > Compressed Folder’. Keeping the default name of ‘package’ for the folder is fine.

3. You are now setup to deploy the destructiveChanges.xml file to Salesforce. To do this, go to Workbench and login with your credentials. It is recommended that you login to a Sandbox instance before you deploy the file to production.

4. Select Migration > Deploy.

5. Click ‘Browse’ and select the .zip package file. Then check ‘Rollback on Error’, ‘Single Package’, and select Test Level with ‘RunLocalTests’. More information on the Test Level can be found here.

6. Finally, select ‘Next’ and then you will notice that the success or error results will be displayed in Workbench once the deployment process has been completed.

This is a very easy way to delete Apex classes and can be very handy if you need a lightweight tool to do the job.

Hope this helps.

Please mark this as solved if it's resolved so that it gets removed from the unanswered queue which results in helping others who are encountering a similar issue.

Thanks,
Nagendra