A maximum of 4 files can be uploaded, the total size of which cannot exceed 10 MB.
Many popular office suite programs (i.e. Microsoft Word, Powerpoint, etc.) have a function for reducing the size of a file. This function can usually be found in the File menu, or as an option in the Save or Save As box. A Google search for the program, version, operating system, and "reduce file size" (e.g. "word 2011 mac os reduce file size") should return some helpful tutorials.
If you have more than 4 files, you should first see if you can combine some of them, until you have 4 or less files.
If you are unable to consolidate your total number of files, or reduce their size, you might also consider removing some of the images or other media. Your instructor can advise you further about what you should include in your assignment.