Has stated, you have to replace the whole content of the memo, but the following will allow you the change a specific word, in a specific line of a memo field.

Private nCount,lcstr
lcstr = ''
Create Cursor mycursor (comments m)
Insert Into mycursor (comments) Values ('There are many ways to get data from a specific line in a memofield.'+Chr(13)+ 'But are there any commands or functions to replace a specific line with a new characterstring, or do I have to replace the whole memofield?')
Modify Memo comments
nCount = Alines(myArray,comments)
For i = 1 To nCount
	If i = 2
		lcstr2=Strtran(myArray[i],'characterstring','character string')
		lcstr = lcstr+Chr(13)+lcstr2
	Else
		If i = 1
			lcstr = lcstr+myArray[i]
		Else
			lcstr = lcstr+Chr(13)+myArray[i]
		Endif
	Endif
Endfor
Select mycursor
Replace comments With lcstr
Modify Memo comments

>Hallo!
>There are many ways to get data from a specific line in a memofield. But are there any commands or functions to replace a specific line with a new characterstring, or do I have to replace the whole memofield?
>If I want to replace the contens of line 67, can I do that without touching the other lines?
>
>Thankyou
>/Kjell