Changing Permissions…

have installed a Google Sitemap plugin to create a Google compliant XML sitemap. I activated the plug-in successfully, but I can’t figure out how to change the permissions in order to generate the site map. This is the error message: ( Could not write into …

The instructions read as follows: Make your blog directory writeable OR create two files called sitemap.xml and sitemap.xml.gz and make them writeable via CHMOD In most cases, your blog directory is already writeable.

Can you tell me how to change the permissions in a step by step manner? I am a novice at such things.

Thanks for your help.