1. Browse to your Crysis level folder (Electronic Arts/Crytek/Crysis/Game/Levels).
2. Backup any existing levels with the same name.
3. Unpack the "mapname" folder from the rar/zip archive into the level folder (Game/LPacifica is all about getting in and searching for some missing people,and, in turn, getting them to where it's safe without escalating the status-quo.