Be sure you backup your theme files before you make any modifications
Look to see what files your theme includes - there may be one called "sidebar.php" (some 2-sidebar themes put the code for both sidebars into one file, some use separate sidebar-left and sidebar-right files)....
This should be the file you'll want to modify. If you're not sure of what code to put there in place of what you have, you can do two things:
1. Find a theme that has sidebars exactly how you want the sections to be and copy those code snippets into your sidebar where you want them - don't copy the whole sidebar.php file as it may contain CSS styles that aren't in your stylesheet - you want just the snippets of code that display what you want;
2. Post as clearly as possible what exactly you want to do and maybe some nice coder will post code for you to copy & paste;
Either way editing your theme file carries a risk of messing it up if you don't know what you're doing, hence the backup.