Delete old bdoc log in smw01

Report SMO6_REORG is what you are looking for, it generally nuke a lot of old data, just give it the number of days of log data you want to keep and it's done.
To be more specific check the source code it does call different report to clean up specific data, e.g. RSMWM_BSTAT_REORG to clean up Bdoc statistics.

It's good practice to schedule SMO6_REORG so it's executed every day deleting old (1 week?) data.