Changing size of image after upload

The problem: After uploading image to wordpress, I want to change a size only for one of the image, which was generated during upload. During upload WordPress generates 3 other images: small, medium and large.

Description: I’ve found in wp_postmeta MySQL table an entry for this file. This entry looks like this:

meta_key: _wp_attachment_metadata
meta_value: a:6:{s:5:”width”;s:3:”800″;s:6:”height”;s:3:”530″;s:14:”hwstring_small”;s:23:”height=’84’ width=’128′”;s:4:”file”;s:38:”2009/02/kruszynski.jpg”;s:5:”sizes”;a:3:{s:9:”thumbnail”;a:3:{s:4:”file”;s:36:”kruszynski-80×80.jpg”;s:5:”width”;s:2:”80″;s:6:”height”;s:2:”80″;}s:6:”medium”;a:3:{s:4:”file”;s:37:”kruszynski-128×84.jpg”;s:5:”width”;s:3:”128″;s:6:”height”;s:2:”84″;}s:5:”large”;a:3:{s:4:”file”;s:38:”kruszynski-200×132.jpg”;s:5:”width”;s:3:”200″;s:6:”height”;s:3:”132″;}}s:10:”image_meta”;a:10:{s:8:”aperture”;s:1:”0″;s:6:”credit”;s:0:””;s:6:”camera”;s:0:””;s:7:”caption”;s:0:””;s:17:”created_timestamp”;s:1:”0″;s:9:”copyright”;s:0:””;s:12:”focal_length”;s:1:”0″;s:3:”iso”;s:1:”0″;s:13:”shutter_speed”;s:1:”0″;s:5:”title”;s:0:””;}}

I want to change the image “kruszynski-128×84.jpg” into “kruszynski-94×84.jpg”. So, I’ve change the name of the file on server, manual change the size to 94×84 and upload new file on server, and change the “width” parameter from 128 to 94.

Result: On page, in place where the “kruszynski-128×84.jpg” image was placed, now I see the image in original size, which is 800×530.

What was tested already: I was trying to change only the filename – result was the same: no thumbnail, original size instead.

Can someone have any idea where I should change some options to change this size?

Thanks in advance for any help