This is called exercising a power of sale. If you refuse to leave the property the mortgagee can have you ejected to recover the property from you, and you will have to pay for the legal costs involved. This amount will be deducted from the proceeds of the sale of the property. The mortgagee does not have a right to your household belongings or your car, so you should remove these when vacating the property. Once you have vacated the property, it can be sold at auction or by private sale.
Most sales are by auction.
When selling the property the mortgagee must take reasonable steps to get the best possible price. This means that competent real estate agents should be employed and that the auction or private sale needs to be adequately advertised. You may have the right to claim damages if the sale is unauthorised, improper or irregular. A reserve price for the property should be set by the mortgagee, taking into account the current valuations of the property, the estate agent's advice, the interests of any other mortgagee and your interest in the property.