howto remove redo tablespace

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Hi all;
In a file_per_table env I had configured InnoDB to separate undo tablespace
files.
innodb_undo_logs  = 64
innodb_undo_tablespaces = 32

do to the heavy write  I had and for performance which I need, decided to
change configuration as:
innodb_undo_logs  = 1
innodb_undo_tablespaces = 16

there are two problem:
1- undo001 file has been grown to 13G!  how can i reduce it size?
2- what would happened if i delete the undo016~32 files?


-- 
Regards,
Ali R. Taleghani