So I when I go into Waypoint I see BPR and the next day I go like I wanna raise my bpr from 51 to 56 but when I try it doesn’t work so can someone explain to me how the BPR works?
Also, I recently changed my GT and my spartan went to default and ever since it won’t update my spartan why is that?
Battle Proficiency Rating (BPR) is a number between 1 and 100 representing a player’s overall skill in Halo: Reach’s Mutiplayer mode. This rating tracks your Kills, Wins, Assists, Deaths, and Betrayals across all matches played. You must play at least 10 Invasion, Arena or Competitive games for this number to be calculated.
Focus on bringing the bold up for it to get higher.
As for your spartan being default, Waypoint takes a little time to catch up with name changes, give it time, should sort itself out 
BPR is directly related to your KD. Basically 1.75 KD and higher KD is 100BPR. It means nothing.