There are two types of upgrades: temporary and permanent.
Permanent upgrades can be stored and reused.

Temporary upgrades CAN NOT BE STORED. If you remove them or swap your sled you will lose them.

Temporary upgrades last only for a limited number of days, these are Klondike days: the number of days it takes to travel to a location.
If you use the plane days are not subtracted from the sled improvements.

You must INSTALL the upgrade. To do this the item must be in your storage. Open your sled, click the team tab, click a plus sign at the bottom to install.