How to change thumbnail size?

I am uploading video and thumbnail is generated.

1. How to setup thumbnail size? For example I want thumbnails with size 300x250 pixels (max dimensions, shrunk proportional to that size if video dimensions are bigger)
2. Is is possible to have more than one thumbnail size? For example for my video - thumbnail one 300x250 and second thumb 60x50. If yes, how to setup, how to get file paths?

3. There are images in /kalturaCE/content/entry/bigthumbnail/... folder, which seems to be in original size of the clip. How to get proper path to those thumbs? In "entry_update" notification, there is "thumbnail_url", but the size is too small for my needs. If 1. and 2. are not possible I need original sized image to create my thumbs manually.

10x