I don't think such a plugin will make any sense (if even possible to create).

You just need to edit the hidden file .htaccess in the Elgg install directory to adjust the upload limit in the line "php_value upload_max_filesize". You also need to increase post_max_size to at least the size of upload_max_filesize (better a bit larger to take into account some overhead). You can also use "M" to indicate the value to be in megabyte, e.g.

php_value upload_max_filesize 100M

would increase the upload limit to 100 megabyte. On the overview page in the admin area of your site you can check the current values used. If the values shown there are smaller than the values you have set in .htaccess, ask the support of your webhoster if they might restrict the limit or if you can't change the php values by using a .htaccess file (possibly you need to change it in php.ini in this case).

Ask your hosting support first about the upload limit. If there is no limit or if it can be easily changed, just do what @iionly said.

yep.. I ask, but say that I have 15 gb in my hosting for upload limit. and I try edit:

php_value upload_max_filesize 

but in server info is: 

What is the limit you want to set exactly? Is it really 15 GB (Gigabyte!)? That's extremely large and I'm not sure any filesystem is able to handle such large uploads in a reliable way (not speaking of available disc space, server ram etc.). Also, you wouldn't have to increase upload_max_filesize and post_max_size but surely also max_input_time (time limit for uploading the file) and max_execution_time (time limit of running time of script handling the upload).

The values you posted above for upload_max_filesize and post_max_size are both around 100 MB. Are these the current values set for these variables in .htaccess? If not, have you defined larger values? In this case your webhoster might have set some maximum values you can't override. If larger values do not work, can you set smaller values? If this doesn't work either, your server is configured in a way that doesn't allow to configure php variable values in .htaccess, e.g. using suphp/suexec. If you can't set the values in .htaccess but have access to the server's php.ini, you can set the values there. If you can't modify php.ini, ask the support of your webhoster how to procede.

What kind of files are you trying to upload? For exampe, both the Tidypics (image uploads) and iZAP Videos (video uploads) have plugin settings to limit the maximum filesize, too. Maybe the limits defined in the plugin settings of these plugins (or some other plugin you are trying to uploads files to) is the limiting factor and not upload_max_filesize in .htaccess.

oh I see. I want to put the maximum value is 200 mb. but I can not configure them.
I try but do not change.
to upload a video of 140 mb, says: maximum value.

Where have you tried to change the value? What value shows up on the server info page in the admin area of your site (http://YOURSITE.URL/admin/statistics/server)? Does the values shown on this page change at all when changing the values of post_max_size and upload_max_filesize? If not, your server doesn't allow changing php values from .htaccess and you need to change the values directly in php.ini as I already mentioned (if in doubt, ask the support of your webhoster).

If using iZAP Videos for uploading the video file you also need to change the maximum allowed video filesize in the plugin setting of iZAP Videos. And it won't work to set this value larger than upload_max_filesize. Does it even work with uploading a video file smaller than the value of upload_max_filesize and the maximum video file limit of iZAP Videos (in case you use that plugin)?

I've tried .htaccess but do not change the settings. I think I will tell the webhoster.

Thanks for your answers.