Go to the layer you want streched in your layers area lol. Then go to the area where there is the marquee tool, if the single row marquee tool isnt there right click it and select it. On the streching layer, use the marquee tool to select a portion of the layer, then hit CTRL T, to transform it. Next do as you would do to inlarge in microsoft word, pull on the little enlargie tabs that popup. Repeat on the other side and there you go a simple pixel strech.