Change the limit of only 100 uploads per bulk upload?
 

Under:

The number of files that you would like to process at a time.
Note: If you experience problems with the page timing out try setting this option to a lower number.

Number of files to process at a time: 100

How can i change 100 into 300?

You can edit your template ADV_GALLERY_UPLOAD template and add an option for 300

I did this for you as a courtesy but we can not support anything if your having timeout issues etc as a result of trying to process this many photos at one time.

Ok mate. You made a good point. I might put it back to 100 later down the track.

No problem enjoy your day