How to relocate the block change tracking file

To relocate the block change tracking file you have two options:

1) shutdown database, mount database, update control file, open database

sqlplus / as sysdba
shutdown immediate
exit
 -- Move the block change tracking file to the new location using the appropriate os utility. --
sqlplus / as sysdba
startup mount
ALTER DATABASE RENAME FILE 'ora_home/dbs/change_trk.f' TO '/new_disk/change_trk.f'; 
ALTER DATABASE OPEN;

OR

2) disable and re-enable block change tracking, and point to the new location when re-enabling.

ALTER DATABASE DISABLE BLOCK CHANGE TRACKING;
ALTER DATABASE ENABLE BLOCK CHANGE TRACKING USING FILE 'new_location';

See Section "4.4.4.3 Moving the Change Tracking File" in the Oracle Documentation regarding this feature.