Out of the box there is no way to delete work items inside Team Foundation Server 2010. Does this mean that it is not possible? No, you still have the Team Foundation Server Power tools which add some commands that allow you to delete work items and work item types.

Here is how to do it for Team Foundation Server 2010:

Step 1: Log-in to the server running TFS using a Team Foundation Server administrator user account.
Step 2: Open a command line and go to:

32-bit machine – “X:Program Files Microsoft Visual Studio 10.0Common 7IDE”
64-bit machine – “X:Program Files (x86)Microsoft Visual Studio 10.0Common 7IDE” (This might change a bit so make sure the path is correct on your PC first)

Step 3: Use the “witadmin.exe destroywi” command in the following way:
witadmin.exe destroywi /collection:http:\[YourServerName]:8080tfs[CollectionName] /id:[WI ID]
You can add as many Work Item IDs as you like using [,] for example 54,88,92 etc.
You can disable the prompt message by using /noprompt.

Example 1: witadmin.exe destroywi /collection:http:\johanServer01:8080tfsjohanColName /id:0,1,2
Example 2: witadmin.exe destroywi /collection:http:\johanServer01:8080tfsjohanColName /id:0,1,2 /noprompt

And that is it, work items will be deleted from Team Foundation Server .  NB!  Deleted work items can not be undone.

Hope this helps!