alter table in hana web based development workbench tutorial

[#1]

please help me for below 2 cases:

1.add new column in table

command which i tried: alter table schema-name.table-name ADD column Source varchar(50);

2.update column size in table

command which i tried: alter table schema-name.table-name MODIFY COLUMN remarks VARCHAR(150);

but i am getting error as :

11:02:17 AM (SQL Editor) Could not execute 'alter table schema-name.table-name ADD column source varchar(50)'

Error: (dberror) 257 - sql syntax error: incorrect syntax near "source": line 3 col 42 (at pos 43) 11:02:23 AM (SQL Editor) Could not execute 'alter table schema-name.table-name MODIFY COLUMN remarks VARCHAR(150)'

Error: (dberror) 257 - sql syntax error: incorrect syntax near "MODIFY": line 1 col 31 (at pos 32)

what is exact syntax for updating existing table.

please help.