CLEAN UNDO TABLESPACE

Question

Hi Group
We need to free up an old UNDO tablespace (TS_ROLLBACK) because we have created a new one (TS_UNDO), ¿how can we do that?, we need to drop old UNDO tablespace but it keeps some extents active more than 4 days.
OWNER     SEGMENT_NAME     TABLESPACE_NAME     EXTENT_ID     FILE_ID     BLOCK_ID     BYTES     BLOCKS     RELATIVE_FNO     COMMIT_JTIME     COMMIT_WTIME     STATUS
SYS     SYSSMU8$     TSROLLBACK     0     51     122     57344     7     51               ACTIVE
SYS     SYSSMU8$     TSROLLBACK     2     104     8969     1048576     128     104               ACTIVE
SYS     SYSSMU215$     TSUNDO     3     107     3593     1048576     128     107               ACTIVE
SYS     SYSSMU229$     TSUNDO     0     107     6370     57344     7     107               ACTIVE
SYS     SYSSMU229$     TSUNDO     3     107     46985     1048576     128     107               ACTIVE
SYS     SYSSMU256$     TSUNDO     3     107     40073     1048576     128     107               ACTIVE
Thank you so much

Answer 1

When I try to drop the tablespace it shows the message:
ORA-30013: undo tablespace 'TS_ROLLBACK' is currently in use.
The result of the query is (i've copied 4 lines of 68, there is a transaction that have started on 15 January, could it be what locking the ts?:
ADDR     XIDUSN     XIDSLOT     XIDSQN     UBAFIL     UBABLK     UBASQN     UBAREC     STATUS     START_TIME     START_SCNB     START_SCNW     START_UEXT     START_UBAFIL     START_UBABLK     START_UBASQN     START_UBAREC     SES_ADDR     FLAG     SPACE     RECURSIVE     NOUNDO     PTX     NAME     PRV_XIDUSN     PRV_XIDSLT     PRV_XIDSQN     PTX_XIDUSN     PTX_XIDSLT     PTX_XIDSQN     DSCN-B     DSCN-W     USED_UBLK     USED_UREC     LOG_IO     PHY_IO     CR_GET     CR_CHANGE
C00000011B25E880     8     26     2204276     0     0     0     0     ACTIVE     01/15/10 18:03:24     135089268     23     2     104     9065     -17910     27     C000000117D19BF8     5635     NO     NO     NO     NO          0     0     0     0     0     0     0     0     0     0     13     23     37359     2
C00000011AC1ED80     271     26     3160     0     0     0     0     ACTIVE     01/21/10 08:00:03     341730228     23     3     107     22901     208     49     C000000117E65CE8     4199939     NO     NO     NO     NO          0     0     0     0     0     0     0     0     1     1     3     257     2492     0
C00000011B1F0A20     251     5     2102     0     0     0     0     ACTIVE     01/21/10 08:04:54     341785988     23     3     107     53963     194     43     C000000117E3D898     4199939     NO     NO     NO     NO          0     0     0     0     0     0     0     0     1     1     11     13     1008162     16
C00000011B25A138     255     5     2932     0     0     0     0     ACTIVE     01/21/10 08:17:49     342060712     23     2     107     3350     331     9     C000000117E1BDE8     4199939     NO     NO     NO     NO          0     0     0     0     0     0     0     0     1     1     3     5     19     0