There are multiple ways to delete a contact. Go in the folders tree view and select the folder where the contact is located. All the contacts for this folder will be displayed on the list situated on the right side of the folders tree.
Then you can do the following:
1. Right click on the contact that you want to delete and choose the Delete option from the displayed popup menu.
or,
2. Click on the contact that you want to delete and then click the Delete button on the toolbar (this is the fourth button on the toolbar)
or,
3. Click on the contact that you want to delete and then go to File menu and choose the Delete Item option.
or,
4. Click on the contact that you want to delete and then go to the Contacts menu and choose the Delete option.
The selected contact will be deleted from the database.