To add services:
To remove services:
Any service you add (through a service provider) to the Service Panel will be remembered next time you start Taverna. If you want to remove such a service, simply right click on it in the Service Panel and remove the corresponding service provider. Note that removing a service provider will remove all services added though it (if there were several), and not just that one service. You can also remove all services you added at once, so only the default ones will remain.
You can also remove the default set of service providers and restore them later on. This is done in a similar fashion by right-clicking and selecting an appropriate option from the pop-up menu. You can further configure the behaviour of default service providers through Preferences (File > Preferences > Service Providers).