MODX doesn't really have a default location and doesn't need to be in a directory called modx (or in a subdirectory).
Do you need to have modx in a subdirectory? If not, you could start over and install modx in the document root, change the setting back, and run the install again. Once everything is working, you could delete the /modx directory from the root.
The basic process is to unzip the MODX .zip file on your local machine and then create a new .zip file in the directory that contains the basic MODX files (/manager etc.). Transfer that new .zip file to the Apache web root on the remote and unzip it there. Then run install (or setup for MODX Revolution).
You could also just move everything in your /modx directory up one level to the Apache web root and run install/setup, but I think the method above would be safer.
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PLEASE, PLEASE specify the version of MODX you are using.
MODX info for everyone:
http://bobsguides.com/modx.html
