Hello,
If you set up the file manager with the correct permissions in combination with the Text Editor, you should be able to upload images through the editor when editing text.
I have just run a quick test and was able to set up a text / HTML module with edit permissions to a security role which allowed that security role to upload and select images.
As a starting point, I would have a look at this video tutorial: The File Manager in DotNetNuke 4.3 and 3.3
Is this what you are trying to achieve or do you also wish to upload documents such as PDF files?
Thanks,