Pentax LX Quick Help/Reference Manual page 18

To change the LX Focusing Screen, use the pincette supplied with your
new focusing screen. Insert the head of the pincette against the top plate of
the mount so that the two ear-like tabs rest again,st the indentation in the
plate as illustrated. Then, gently lift upward on the handle of the pincette
until the focusing screen frame drops down.
CAUTION: Move the pincette very carefully. If the screen doesn't release
immediately, do not exert excessive pressure: a slip could damage either
the focusing screen or mirror surface.
Squeeze the handle of the pincette and very carefully sandwich the tab of
the focusing screen between the two sections of the head. Lift the screen
out of the frame and place it in the container for protection.
To install the new focusing screen: Pick up the screen by the tab with the
pincette as described above and place it on the focusing screen frame with
the tab on the right hand side as shown. Push the frame back to its original
position until it locks in place.
IMPORTANT: Only handle the screen with the pincette and hy the tah
only. Never wipe screen surfaces with clothing or a cloth to avoid
damage. Remove dust particles with a blower or camel's hair brush.