The assumption is that you deployed your branding solution as .wsp file and you now wanted to make further changes such as the master page, page layout, CSS, images etc..
How do you go about the upgrade and deployment process:
- Open your existing branding solution using Visual Studio 2010 or latest version
- Make the appropriate code changes
- Save your project and later, right click your solution and “Rebuild”
- Right click your solution and click “Package”
- Right click your solution and click “Open Folder in Windows Explorer”
- Click the bin folder
- Click Debug folder
- Make sure your .dll, .pdb and .wsp files’ modified date is todays date to reflect that you indeed have rebuilt the project
- Make a copy of the wsp file, rename it such as by giving a version number
- Since this is a Sandboxed solution, to deploy click Site Actions -> Site Settings -> Solutions (i.e. under Galleries)
- From Solutions page, click the Solutioms ribon and later Upload Soltuion icon.
- Upload the renamed .wsp file and in the Solution Gallery – Upgrade Soltuion dial box click the Upgrade icon
- As you can see your new .wsp file is activated while the previous .wsp file is deactivated
That is it.