Upload your PowerPoint to a document library, then open it in web view. Now, go to File and choose Share.
On the Share page select Embed.
You will see options for the embed size, as well as the generated code to include in your page.
Pick the appropriate size (2nd or 3rd work best), then select all the text in the Embed Code box. Click on Close.
Now go to the page where you wish to embed the document and edit it. Click where you want to embed it (in Page Content), or optionally, add a Content Editor web part in any available zone. Once you've placed the cursor where you want the embedded document to show, click on the Insert tab, then click Embed Code.
Paste the code into the appropriate text box, and click Insert. You'll notice that the dialog updates itself when you add the embedded code
Publish the page, and you're done! Don't forget to enter comments in the Publish dialog to leave a note on what you updated.