Do you mean MySQL 5.0.92 or MySQL 5.5 latest?
For upgrade to MySQL 5.0.92
If you change versions, I would recommend that you setup a virtual machine (VM) where you install a test setup, so you don't mess up your production environment.
- Install your OS in the VM (same version as on the production machine.)
- Install MySQL (same version as on the production machine).
- Restore your database, grant tables and my.ini on the VM
- Check that your database works the same on the production machine and the VM.
- You now have a test setup that you can use as a starting point.
- Make a full backup of the VM (this is called an image).
- Upgrade MySQL on the VM
- Restore the database on the VM
(if needed, should not be needed for an upgrade from 5.0.26 to 5.0.92)
- Test to see if everything works the same on the VM as on the production machine.
- If everything works: Make another image of the VM.
- Make a full backup of the production machine. (OS, MySQL, data, ... everything).
- Remove the hard disk from the production machine and insert a new blank harddisk
- Restore the backup made in step 11 to the new harddisk.
(You now have a full backup on the old harddisk that you can fall back on if need be).
- Test to see if everything works, you can use the VM to compare if need be.
- Now you can upgrade your production machine to 5.0.92
Upgrade to MySQL 5.5 latest
For upgrading from 5.0 to 5.1 read this:
For upgrading from 5.1 to 5.5 read this:
First upgrade from 5.0 to 5.1.
Then upgrade to 5.5.
Remember to use the steps above to make sure you don't lose any data.
And keep backups of every step. do not overwrite media
And remember a backup is not a backup unless you have successfully restored it!