Remortgaging is the replacement of an existing mortgage with a new one. The existing mortgage is repaid when you complete on the new loan.
You may be remortgaging to save money or to reduce your mortgage term. This might be possible by switching to another mortgage product with the same lender or by switching your business to another provider. Remember, if you switch lenders, the saving you make on the interest rate you pay may be partially or wholly eaten up by the transaction charges associated with moving your loan.
There are other considerations to take account of too. Your existing lender may demand redemption fees, and may charge you a penalty. The new lender may charge an arrangement fee and will want to value the property just as your old lender once did, so there'll be surveyor fees as well as solicitors’ fees to factor in. There will also be the cost of search fees and a Land Registry fee to pay to register your new lender.