txt_welcome is a language variable. you can use the WYSIWG editor in x-cart to get some idea of what it will look like, or you can just paste what is there to a good text editor (I prefer PSPad (
www.pspad.com) , add <html> and <body> tags, save it as a html page and look at it in a browser (or in PSPad, there is a view as html button).
Once you are satisfied just copy between the <body> tags and paste it into the x-cart txt_welcome languages box.
I don't really like FTPeditor because the changes you make are pretty much immediate, and if you screw up too badly it is sometimes very difficult to fix.
To clear the templates cache, there are 3 ways... enter
www.yoursite.com/cleanup.php in your browser... in admin click summary, then tools, scroll down to "clear templates cache" and click "clear", or using FTP, delete all of the files in var/templates_c folder.