1.. Connect to root container as sysdba then show pdbs
2.. First shutdown pluggable database and then open in restricted mode for e.g NONPDB4
3.. Now connect to Pluggable database NONPDB4 that you want to change the name.
4.. execute alter pluggable database rename global_name to DEMO;
Note :- There will be change in name of PDB but not with CON_ID, directory where datafile of PDB resides.
Happy Learning !!!!