Clearer and more consistent phrasing

wiki/src/upgrade.html

@@ -30,8 +30,8 @@ following them:</p>
     <h4>You need:</h4>
 
     <ul>
-      <li>Your USB stick</li>
-      <li>Another USB stick with Tails up-to-date</li>
+      <li>Your Tails USB stick</li>
+      <li>Another up-to-date Tails (USB stick or DVD)</li>
       <li>¼ hour to upgrade</li>
     </ul>
 
@@ -50,7 +50,7 @@ following them:</p>
     <h4>You need:</h4>
 
     <ul>
-      <li>Your USB stick</li>
+      <li>Your Tails USB stick</li>
       <li>Another empty USB stick <small>(at least 4 GB)</small>&nbsp;[[!toggle id="why_extra" text="Why?"]]
 
         [[!toggleable id="why_extra" text="""