You need to use an FTP client like filezilla or in windows explorer you can put ftp://yoursite.com in the file path and login that way. Your hosting provider may have an online ftp client as well.
I also like to use Google Chrome to right click on features of a page and use the inspect element tool to find which css file is affecting what. As well you can test change values and see the changes in real time without actually changing the css file. I use this to avoid editing and uploading the css file over and over.
I've learned all this on my own as I am just starting out as well and I'd be very interested in what a more experienced developers workflow is like.
I also like to use Google Chrome to right click on features of a page and use the inspect element tool to find which css file is affecting what. As well you can test change values and see the changes in real time without actually changing the css file. I use this to avoid editing and uploading the css file over and over.
I've learned all this on my own as I am just starting out as well and I'd be very interested in what a more experienced developers workflow is like.
public_html/packages/your theme/themes/your theme/css files is what it usually looks like
To edit you are going to want a developer console to try different edits, and locate the right codes to change
Use this video for a full breakdown (only 6 minutes)
http://www.youtube.com/watch?v=3KdNRZS-uSg...
Once you have the developer firebug or other depending on browser, its just a matter of opening the right css files and editing in notepad. This can be done from your cpanels file manager or ftp like filezilla. Open the css file for what you want to change find the line you want to change, and edit it. Save your edits, and they will instantly appear on site on refresh.