In order to customize the theme color, you need to go to the site editor, there will be a "Customize" column and there you will need to select the color of the desired theme. You can find more colors for your themes on the service ....

Thanks Ermin,

I was trying the same way but the change is not taking effect after selecting the color and trying to load the color came back to orginal.

I think there is an additional step to unlock the them.

I`m using Odoo Expert theme

BR
Samir BECHAR

You can customize your theme when editing your website under "Customize/Customize Theme":

Then you get the customizing options:

Changing the logo size is not simple and needs some knowledge about theme development and bootstrap. For reasons of responsiveness, I do not recommend to change the logo size, if you still want to do it, use media queries for proper responsiveness.

Can you be more specific about what does not work or what you want to achieve?