How to change oracle max connection limits for "maximum connection exceed problem"?

$ sqlplus
Enter user-name: sys as sysdba @sys
to see parameter process for altering system sessions (processes (integer) = sessions)

SQL> show parameter session 
SQL> ALTER system SET sessions= 300 scope=spfile;
SQL> show parameter process
SQL> ALTER system SET processes= 300 scope=spfile;

Finally, restart the database to activate all changes