The Force.com platform has a limitation of 25MB (max.) per attachment for the 'Notes and Attachments' related list.
There is no way to increase the amount of data for attachments. Using a compressed PDF could help reduce the size of your files. With a quick search for PDF shrinker or compressor on google you could find various programs that can do this, many for free. This could be an option to get your files lower than 25MBs.
If the file is for the whole company you can upload them to the Chatter Feed. This will make it available to all users unless you specify a private group in Chatter, but won't be associated to any specific record. The maximum size of a file on chatter is 2GB.
Please review more details in the table in this documentation link.
To see your total storage limit, go into Setup> search for Company Information > Used File Space. To see where the files are select View after the Used File Space.
More about the Property Media Manager limits here.