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I'll give this a shot, having just done this myself. I'm going to assume you are using an iPhone. If not, I'm not sure how much of this will apply.
Slide the UP Feed screen to the right to reveal the sub-menu.
Choose the team member you want to delete
Choose the Gear Icon in the upper right-hand corner of the team member's window
Choose 'Remove Teammate'
The team member will be removed from your list... BUT, it will take some time for the database to propagate this change. When I deleted a teammate, they were still able to comment in my UP Feed several hours after the deletion (meaning they still saw me as a teammate for several hours after I deleted them). The deleted teammate's data should stop posting to your UP Feed, BUT, their past entries on your UP Feed will remain (at least that's how it is for me). I hope this helps!
Sorry! I misunderstood your initial questions. Unfortunately, I have no experience with adding team members through the iPhone Contact List, Facebook or Twitter. None of my contacts are using the UP Band
If this works like other apps, I would assume you will need to invite and confirm individual names that appear in the 'Matches' list. You shouldn't have to worry about removing people you don't want to team with from the list, because your not going to invite them as a group. Any names that appear in the 'Matches' list are simply received from either your iPhone Contacts, your Facebook friends, or your Twitter followers.
If you want to remove your iPhone contacts from the 'Matches' list, you need to turn off sharing with the UP App. You can do this by going to Settings | Privacy | Contacts. There, you will find an on/off switch for the UP App. You will most likely need to go through control panels in Facebook and Twitter to turn off sharing for those apps.
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