Getting error while installing log4db2 utility DB21034E  The command was processed as an SQL statement because it was
  not a valid Command Line Processor command.  During SQL processing it
  returned: SQL0601N  The name of the object to be created is identical
  to the existing name "LOG_CONF_BP" of type "BUFFERPOOL". 
  SQLSTATE=42710


How to remove pre-existed "LOG_CONF_BP" of type "BUFFERPOOL" in db2 database? Is there any other way to define logging for my stored procedures?
LOG_CONF_BP is a bufferpool. That is a chunk of memory dedicated to doing something (usually servicing one or more tablespaces, which is where tables reside). So what is happening is your stored procedure is trying to create an object that already exists. 

So what is going to need to change is the stored procedure. I would ask if your stored procedure needs that exact bufferpool or not. If yes, then change the stored procedure to check for the existence of LOG_CONF_BP (you can check against syscat.bufferpools for that). If it doesn't exist, create it, otherwise don't.

Otherwise, even if you drop the LOG_CONF_BP, so your stored procedure succeeds, it will just fail again the next time you run it anyway....