ARBs result in the following changes: increased renin, increased Ang I, increased Ang II, decreased aldosterone and unchanged bradykinin

A good way to think about this is that angiotensin II is present at the ANGII receptors. If you give an angiotensin receptor blocker such as losartan. this will displace the angiotensin II present in the receptors. thus increasing the levels of angiotensin II in serum.