Currently the maximum file upload size for any user is 10mb. That’s a really huge file and not recommended if have many users accessing your website with upload capability. You will want to decrease this maximum to a reasonable size like 5mb or even 1mb. You can easily accomplish this by using the Media Manager.
Media Manager Options Manages Images:
1. Login to your Joomla 1.7 administrator backend
2. Click on ‘Content’, ‘Media Manager’
3. Click on the ‘Options’ button at the top right
4. Under Media Manager Options, set the following value:
Maximum Size (in MB) = 1
5. Click on ‘Save & Close’
After you save your options then the image file cap will be set at 1mb. Users uploading images with file size greater than the maximum will be given an error message, see the screenshot below that says:
This file is too large to upload