mysql - replace text based on another column value -

first time post , looking little bit of help, i'd grateful if advise me,

i have table on server, eg:-

column column b
column c 1
30-08-2015 hello
42 3
30-08-2015 hello
45 2
30-08-2015 hello
20 4
30-08-2015 hello
1 1
30-08-2015 hello
32 1
30-08-2015 hello
21 2
30-08-2015 hello
21 3
30-08-2015 hello
0 4
30-08-2015 hello
21 1
30-08-2015 hello
24 1
30-08-2015 hello
67

i looking command change column b 30-08-2015 bye when column = 1

i've found few replace statements doesnt take account value of column a. advice??

i'd @ mysql update command. allow

update table  set b='30-08-2015 bye'  a=1;