Thank you so much JAVesey!
I had the settings for "Check templates for modifications" set to "No". After I set it to "Yes" I was able to make changes to my theme.html and therefore set up the width and size. Thanks a million guys.
P.S.
I do translations from Czech-English, English-Czech so if anyone needs help with translations I'd gladly contribute.
Thanks again!

I have a question about where to go when I need to adjust the parameters of individual logos.
Each theme has its own default logo that I'd like to replace or customize it to my needs.
I tried to change the size of the logo in photo editor and that didn't do it.
Then I tried to go to theme.html to look for the line, where I could adjust the width and height.
But when I do that the changes don't reflect when I reload the page.
Checked stylesheet and didn't find it there.
The part of the code that might have something to do with it is <{$xoops_url}> and <{$xoops_imageurl}>
Where are those locations?

The full link is here:
<a href="<{$xoops_url}>/"><img src="<{$xoops_imageurl}>images/logo.gif" width="150" height="50" alt="Logo" /></a>

Does anyone have an idea?

Man, there is a lot that I need to learn too