php - Replace a word in column that have much content -

want know how can change word in column text have words.
example have

|id|             content             | | 1| name alpha root .. | | 2| need alpha root  | | 3| today alpha root     | 

i want query can me change alpha beta in content , keep other things.
become

|id|             content             | | 1| name beta root ..  | | 2| need beta root   | | 3| today beta root      | 

i have researched lot no results

update your_table set your_field = replace(your_field, 'alpha', 'beta') your_field '%alpha%' 

source : http://dev.mysql.com/doc/refman/5.0/en/string-functions.html#function_replace