Hi Giannis,

I assume that the lines either end with a paragraph mark ? or a hard line
break (an arrow pointing down and to the left).  For the former, you can use

^p<space><space>          i.e. ^p followed by two spaces

in the Find what box of the Edit>Replace dialog and use a single space in
the Replace with box.

If it's the latter, use

^l<space><space>        that's a lower case L

in the Find what box

Please post any further questions or followup to the newsgroups for the
benefit of others who may be interested.  Unsolicited questions forwarded
directly to me will only be answered on a paid consulting basis.

Hope this helps
Doug Robbins - Word MVP