The only way I know how is to copy the 52 MB file five times. Edit one of the copies. divide the number of pages in the manual by 5, lets just say it is 75 pages. Find the first 75. DELETE the rest of the file. Save the results. Before you go any further try to post up the 75 page attachment. If it works (I doan tink it will but maybe) carry on. If not cut that 75 pages into 40 and see if you can upload it.
Edit the 2nd copied file. Delete everything past page 150. Then delete the first 75. Get the picture on the steps?
You will end up with 5 (could be 10 or 20) approx equal size files and even at 10 MB lots and lots of email systems will tell you go away.
You may have to post up one segment for a day or two or three then delete it and repeat.
Best of luck