The default database prefix is "ubbt_" and generally does not need to be changed, unless you're running multiple copies of UBB.threads.
In the code the database table is "ubbt_FILES", db prefix "ubbt_", so if your prefix in your config is "morgan_" the table would be: "morgan_FILES", likewise "morgan" would be "morganFILES".
The easiest thing to do would be to load PHPMyAdmin and look for the FILES table and use that.