Oracle 18c

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CREATE TABLE tjson ( jsoncol CLOB CONSTRAINT tjson_chk CHECK (jsoncol IS JSON) );
BEGIN
 INSERT INTO tjson (jsoncol) VALUES ( '{"name" : "Kunal", "LName" : "Vohra" , "salary" : "10000", "Age" : "25"}');
 INSERT INTO tjson (jsoncol) VALUES ( '{"name" : "Rahul", "LName" : "Sharma" , "salary" : "20000", "Age" : "35"}');
END;
/
1 rows affected

SELECT *
  FROM tjson;

JSONCOL

{"name" : "Kunal", "LName" : "Vohra" , "salary" : "10000", "Age" : "25"}

{"name" : "Rahul", "LName" : "Sharma" , "salary" : "20000", "Age" : "35"}

UPDATE tjson 
   SET jsoncol = REPLACE( jsoncol, '"salary" : "10000"', '"salary" : "15000"' )
 WHERE JSON_EXISTS(jsoncol, '$.name?(@ == "Kunal")'); 
 
1 rows affected

SELECT *
  FROM tjson;

JSONCOL

{"name" : "Kunal", "LName" : "Vohra" , "salary" : "15000", "Age" : "25"}

{"name" : "Rahul", "LName" : "Sharma" , "salary" : "20000", "Age" : "35"}