Increase Image Size

Hi Hope someone can help please.

I am working on a charity site where I have developed a directory of members for the public to find a member in their area and/or country to do this I used a plug in called ‘Participants Database’. Presently when I add an image to the member file in this programme it publishes a miniscule image where I really wanted an image of some 250×200.

The author of the plug in has suggested that I could put a command in the CSS file of the Theme and he has suggested something like

#content .pdb-single .image-field-wrap img {
height: 3em;
}

Unfortunately I am not familiar at all with CSS and I do not want to damage my site. Could anyone give me guidance of what I should do.

In the settings of the plug in I have set the file upload to 500k which governs the maximum file size for an uploaded image but this made no difference. A sample of what happens can be found at ‘http://eac.eu.com/newsite/find-a-counsellor/individual-accredited-member-details?pdb=76’

Any help warmly appreciated.