e.g.
Backup database
RMAN> backup database
Mount database
SQL> shu immediate;
SQL> startup mount;
Change DBID
$ nid TARGET=SYS
or
Change both DBID and DBNAME
$ nid TARGET=SYS DBNAME=new_xe
Change database name from parameter file (init.ora)
*.db_name='NEW_XE'
Mount database again
SQL> startup mount;
Open database
SQL> alter database open resetlogs;
Ref: https://docs.oracle.com/database/121/SUTIL/GUID-05B4733C-9EAA-438F-A2A4-4E84EB1E1E65.htm#SUTIL1544s