There are several options:
1) You can purchase a new place and rent it out for 6 months, while you are selling your current residence. Mortgage calculation takes 75% of gross rental income as additional income, so you'll have to qualify.
2) You can purchase a new place, move there, and rent out your old place (same for the mortgage calculations) for 6 months, while you are selling.
3) You can buy with contingency to sell your old house, as Abeda mentioned
4) If you can take cash out of your current home, and pay off the new (downsized one), so there are less expenses. You'll refinance the new place later on, if need be. Depending on your agen, reversed mortgages could be yet another option.
5) You can move somewhere else (relatives, friends, kids), if possible, and rent out both places untill you sell the old one
6) You can stay in post-occupancy period, which could be a couple of months...to buy a new downsized place
Hope this helps.
Irina Karan, CDPE
Beachfront Realty, Inc.