cfg/stats.txt :  

"stats"  
{  
      "STEAM_1"  
      {  
          "k" "1"  
      }  
      "STEAM_2"  
      {  
          "k" "2"  
      }  
      "STEAM_3"  
      {  
          "k" "3"  
      }  
}  

Удаляем STEAM_2  

#include <sourcemod>  

public OnPluginStart()  
{  
      new Handle:kv = CreateKeyValues("stats");  
      if (FileToKeyValues(kv, "cfg/stats.txt") && KvJumpToKey(kv, "STEAM_2"))  
      {  
          KvDeleteThis(kv);  
          KvRewind(kv);  
          KeyValuesToFile(kv, "cfg/stats.txt");  
      }  
      CloseHandle(kv);  
}