Hi Chinmoy, thank you for the answer but I guess I should have asked for more specific information that simply “pointing me in the right direction”. Sorry, but I am not a developer, just a user who is able to make changes to .php and .css files upon instructions.
After reading the link you sent this seems like a really complicated process with changes to several files. (When did WordPress grow so unwieldy?). All I want to do is change one parameter of one preset image size.
Can you please let me know in which file the default image parameters are set, specifically for the 3-column “img-3-columns (345×185)” default size? I have checked several files but cannot locate this. I just want to change it to “img-3-columns (345×245)”. I have tried just using the FULL size with images at those exact dimensions, but the third “Featured Page” widget does not fit onto the same row as the the first two, hence the need to modify and use the “img-3-columns” preset.