There are two parts of upgrading. First part is upgrading the core and second part is the theme. For upgrading the core, a guide has been released by Cosmin.
For Upgrading your theme, writing a guide is not possible as every theme is different for which code change can't be generalised. Try reading the code changes from SVN Changelogs. Changes for 1.8 start from r135.
The default password for the admin account is admin.
With version 1.4 or later, goto the admin login page at http://localhost/jobberbase/admin, login with the default username and password admin:admin, then on the top right click 'Change your password'.
Open _templates/<themename>/job-details.tpl and find the following line:
You can add/edit extensions in this line to be accepted while applying.
Also you will need to edit the text shown below the attachment box too. For that open _includes/translations.ini file and find this line:
Change this too according to extensions enabled above.
Assuming your URL is http://localhost/jobberbase/, the stats can be accessed at http://localhost/jobberbase/admin/stats/.
Assuming your URL is http://localhost/jobberbase/, going to http://localhost/jobberbase/companies/ will show a list of Companies using the job board, and the number of jobs they have posted.
The admin area demo is located at http://www.jobberbase.com/demo/admin (user: admin, password: admin)
First you'll have to create the pages in the backend and make sure all necessary fields have a value. You will then have to create its link to be shown in header/footer or sidebar menus by going to Admin>>Links. (This works only on v1.8 and above. For versions below, you will need to edit header.tpl and footer.tpl to show links to created pages.)
Primary menu is the header menu, secondary menu refers to sidebar and there are 3 columns for footer menus.
Select any menu where you want the link of page to appear and give the url, link title and link name. If the url is internal, you can use the relative path to your jobs site or you can enter the fully qualified url of the page.
Go to your root folder from locahost (for testing versions) or ftp location on your server and find the logo file usually located in "_templates/default/img/jobber-logo.gif" where jobberbase is the name of your site domain folder which will be different for you depending what you name you gave for the folder "app" during installation.
Now there are couple things you can do:
1. Use image editing software like Adobe Photoshop or free GIMP and create a logo for your site with same dimensions (375x82) and replace the original logo file with your custom file but do not change the file name or extension (.gif).
2. Open the screen.css (found in the "_templates/default/css" folder) file with your favourite text editor (I use Notepad++ which is free and can be downloaded from this link » ) and look for this line:
This code in the CSS file:
Now changes to:
Code appears in one line in css file for compression reasons and indented here only. Change the image reference in the "background: url()" property to point to your own custom logo file (now it can be any file name or image extension like png, bmp, gif, jpg etc). Make sure the folder path is correct ("../" means go to root of the site)
Save and refresh your Jobberbase homepage to find your new logo on your jobs site.
If you want to choose between existing themes, go to Themes.
The official forum to find Jobberbase developers is here: 
2. Customize >