Upgrading WordPress is usually a very easy thing to do, and should be trouble free. Normally, an upgrade only takes around 30 minutes or less to complete, provided you plan things in advance. Most of the work involves making site backups and then later uploading everything.
Basically, any WordPress upgrade involves two VERY important keywords:
- Deactivate all plugins.
- Backup everything, especially the wp-config file and the MYSQL database.
If you have planned your theme layout using a WAMP stack like XAMPP for example, you can test out plugins and layouts on your localhost PC. You can try doing it all on a tiny USB flash drive which is pretty hip, but of course for all this, you’ll need some working knowledge of PHP and CSS, in order to run.
When it comes to changing themes, the only thing that needs doing is tests, tests, and more tests. To that end, two Firefox extensions come in handy to me, one is ColorZilla, an advanced eye-dropper tool that integrates with your Firefox browser and provides on-the-spot HTML color code reading of any color you see on a web page.
The other one I use is CSSViewer, which makes estimating pixels of CSS blocks a real snap. It also shows the color of a certain div (just point your cursor at any block), but it doesn’t display pinpoint-sharp pixel color information as ColorZilla does. Both these tools are tiny unobtrusive tools that integrate seamlessly with your Firefox browser.