I have several websites hosted by the same company. Now when I use DreamWeaver 5.5 to visit these sites, I can see the files on the server and I can see my local files. But when viewing local files, I need to be able to Check Out files, edit them, save them and then check them back in so they get uploaded to the server.
In my current state, the Check Out File(s) icon is grayed out.
Go to Site > Manage Sites and choose the one you want to add Check In/Out to.
Go under the Basic tab and hit Next until you get to "Do you want to enable checking in and checking out..." switch the radio button to Yes.
Note: this is how you would turn it on in DWCS4, I'm assuming 5 isn't much different.