Why won’t my wiper sit flush?

Hi guys i’m just wondering why the wiper on my 2005 honda civic won’t sit flush on the windshield… If i push it down it’ll go flat but once i actually use my wiper it just goes back into that curved position and doesn’t clean very well. I’m suspecting the wiper arm may need to be changed?? If this is the case, why do you think so and is it easy to replace myself?

Thank you!