do you have a source code of MonoX, or is it a free version?
If you have a free version, you need to use custom localization solution, change the resources there, build and copy it's bin folder to your MonoX bin folder. More details can be found here
Regarding the text in Default.aspx, please check if you are changing the text inside the MonoX Editor, in that case you need to login as admin and reset the content of the editor. Please let us know if that is a case and we will provide you with more information on how to do it.