You can reduce the file size and save disk space by compressing pictures in your document. The compression options reduce both the file size and picture dimensions based on how you intend to use the picture, such as viewing on screen or in an email message. You can compress all pictures in the file or just the ones that you select.
These features aren't available in Office for the web, only the desktop versions of the Office suite.
Compress all pictures
1. File-->Compress Pictures-->Pircure Quality-->150 ppi
2. Then save as a rename file which is more smaller can upload to some limited file platform.
Compress individual pictures
To compress all pictures in your document, on the ribbon, select File > Compress Pictures (or File > Reduce File Size).
To compress only selected pictures, hold down SHIFT, click the pictures you want to compress, and then click Compress Pictures on the Picture Format tab.
Select an option in the Picture Quality box. Highest resolution is listed first and the lowest resolution is listed last.
Tip: If you have cropped any pictures, you can reduce the file size even more by selecting the Delete cropped areas of pictures check box.
Click Selected pictures only or All pictures in this file.
Note: If you use the Filemenu to choose all pictures in step1 these options will be unavailable. Compression will be applied to all pictures in your document.
Article reprint from Microsoft O365