Plexiglas, also known as acrylic glass, is a plastic substance made from primarily acrylic. It is more durable than glass, easier to cut, and easier to replace. However, cutting it can be tough if you have never done it before.
A plastic-scoring blade can be used. With a straightedge as a guide, pull the blade toward you, leaving a score mark. Score the acrylic several more times along the same line, then place the acrylic on the edge of the table and use light, quick pressure to snap the piece in two.
You can also cut acrylic with more traditional blade tools such as a jigsaw, band saw, or table saw.