United SWU can be used to upgrade on LH. If you're not 1k you'll have to find someone to gift you one or get from him a different way...
You need it a bit in advance because United actually sends out a paper certificate for the LH upgrade.
They can only be applied at the the airport on the day of travel.
If you are getting it from someone else make sure they know what they're doing or to find out all the details regarding LH upgrades.