Whenever you have a contract with a service provider, you're entitled to get the service that you were promised and which you contracted for.
You're also entitled to have that service provided with reasonable skill and care. If you don’t then your broadband service provider could be in breach of contract.
Whether or not your broadband provider has breached the contract, will depend on exactly why you're experiencing slow speeds or interruptions to your service, how frequently it happens or how long you are without a connection.
If you're experiencing regular interruptions to your broadband service then check that it's not due to factors outside your provider's control such as the router, the way you've set up your broadband or a problem with your phone line.
Sometimes this won’t be apparent until someone checks, so you may need to get an engineer to take a look for you.
If the interruptions turn out not to be down to your broadband provider, you'll probably be responsible for the engineer's call out charge.
These providers must give you the expected range of maximum speeds for your line at the point of sale. They must help you with your speed issues, and if your speed remains below your minimum guaranteed, they must let you exit your contract penalty-free. Or alternatively you can agree to continue the contract at a lower monthly cost.
You can find your minimum guaranteed broadband speed in the information your provider sent you after the sale or upgrade.
And if you want to change broadband supplier you only have to notify the company you wish to move to. Your new supplier will then handle every aspect of the change.