It is possible to switch life assurance cover - nothing to stop you as long as you make your lender aware and have the new cover assigned to the lender when you do so ie if the lender requires life cover in place.
A few things to consider - the cost of life cover increases with age so reapplying when you are a couple of years older will affect your monthly premiums. You may find you are not necessarily saving by changing companies. Every application will be newly assessed. As you get older health problems may arise which must be disclosed and will be taken into account when being underwritten. Any health issues deemed higher risk will have a premium to reflect it. Serious health issues may result in the application being declined.