Master slides

Hello Marketa

Thank you for your question and welcome to the forum.

Once you are in the master slide (View-Master-Slide Master), then go to Format - Bullets and Numbering.

After selecting the type of bullet you wish to use, there are settings at the first dialogue box to be able to change the colour of the bullet, and it's size in comparison to the text next to it (under the gallery of default bullet types).

Once you have changed size and colour, click OK.

Kind regards
Amanda