Find and Replace in Mysql Query with Example

Syntax:
update [table_name] set [field_name] = replace([field_name],'[string_to_find]','[string_to_replace]');

Example:
UPDATE system SET filename = replace( filename, 'sites/all/themes/gemswebsitetheme', 'sites1/all/themes/gemswebsitetheme2' ) ;