how to replace the caracter ' with the function txtreplace?

hello, i have a string where there is the caracter '
i want to replace it by another caract, with the txtreplace function.
i tried diferent codes but it does not work...
i tried for example these lines of code :
txtreplace(myvar2, myvar1, ''', 'othercaract');
txtreplace(myvar2, myvar1, ', 'othercaract');

i tried the unicode ('), and the hexacode (%27) too, like this:
txtreplace(myvar2, myvar1, ', 'othercaract');
txtreplace(myvar2, myvar1, ''', 'othercaract');
txtreplace(myvar2, myvar1, %27, 'othercaract');
txtreplace(myvar2, myvar1, '%27', 'othercaract');
but it doesn't work...
If someone has an idea ?
thank's a lot in advance

the unicode for ' doesn't appear in my message, it's (with no space)
& # 3 9 ;

YYYYEEEEEEESSSSS! thank you very much