Hi rayvan22, if you visit Appearance->Themes in your admin area, does it show Twentyeleven as the current activated theme? If so and by looking at your site, then yes you have definitely customized the theme.
Essentially if you activated the Twentyeleven theme and then went to Appearance->Editor and made changes that way.
To preserve your changes you'll need to look into creating a child theme (http://codex.wordpress.org/Child_Themes) and then transferring the changes you made over to the child theme. I'm not all sure how many changes you've made so you'll have to figure that out for yourself.
In short, do NOT upgrade to Twentyeleven 1.4 or you will lose your customizations.
In response to ayuba, if you cannot access the admin area of your site you'll need to FTP into your server and navigate to the easel theme directory and edit functions.php. You'll need to undo the changes you made that way to get your site working again.
You can also just change the name of the easel theme folder and that will deactivate the theme. You can then delete the easel theme, reinstall it and try making your modifications again.