I am not really sure what you mean by "access my download area" as there are a handful of service providers out there that operate in a non-standard way and you may be stuck with one of those. Those, of course, are the ones that target the novice market.

Typically uploading and downloading is done in the same way with an FTP program. Any search engine will find you a selection of FTP software both free and paid for. You need to contact your web host to get the information to set up the software as that will be specific to your account with them.

PDF files are not meant to be changed, that is the whole point of using them. You should have the original document in a word processor or spreadsheet. Change that, save it as PDF then upload it. You may need additional software to convert the file to PDF, obviously I don't know what was bundled with your PC when you bought it and what additional software you have installed.