This is really the first thing you should do after you’ve installed Dropbox. Most people keep all their files in the Documents folder on their PC or Mac, and as these files are usually quite small, you can probably sync the whole lot to Dropbox.
On a PC, right click on the Documents folder and click Properties (For Mac users, it’s Get Info). If the total size is under 2GB, you can sync it all. If not, you’ll need to get more Dropbox space or move some files out of your Documents folder. All done? Then let’s get cracking.
Making Dropbox your Documents folder on a PC
In Windows, open Explorer, right click the Documents folder and click Properties. Select the Location tab and click Move. Go to your Dropbox folder and click OK to select it. All the files in your Documents folder will now be in your Dropbox folder.
Making Dropbox your Documents folder on a Mac
The process on a Mac is a little more technical. First, you need to open Terminal (type Terminal into spotlight). If you have Dropbox installed at the default location, type cd dropbox and click Enter to switch to your Dropbox folder. Then, copy and paste the following command:
ln -s ~/Documents/ Documents
Press Enter. You’ll see a new Documents folder in Dropbox with a black arrow icon, which shows it’s a synced folder. Anything in your Documents folder is now in your Dropbox folder. And every document you work on and save will automatically sync to Dropbox.
Updated 2/19/15 with updated screen shots and detailed instructions.