My taskbar suddenly got higher, taking up more room at the bottom of my screen. How can I control its size?

   It sounds like you accidently dragged the top edge of the taskbar up.
   To put it back down, move your cursor over the top edge of the taskbar.  The cursor should turn to opposing arrows pointing up and down.  Press the left mouse button and hold it down.  Move the cursor down, which should also move the top edge down, to where you want it and release the left mouse button.  That should do it.

Thnanks for the tip...BUT my opposing arrows will only move up. THey work in other situations, like enlarging my web pages on the screen, but not on the taskbar. Thank you in advance.

Your taskbar may be locked.  Right-click on your taskbar and uncheck the Lock Taskbar option.  Then try the dragging the arrows.  
Laverne

This is another try to solve your problem.  There is a good discussion about this problem at the site shown below.  You may find the solution there.
Laverne

http://help.lockergnome.com/index.php?s=f09b65cff11fa0a4424d6265d151c8e0&showtopic=16260