If you are starting from scratch, you may want to consider doing a Hard Reset, this will wipe all of your step fathers data and any changes he might have made to the device.
After a Hard Reset it will be as it was when he took it out of the box. Any extra software that he may have installed would be removed and all the original software and settings would be restored.

But first, you may just need to do a Soft Reset to get things running again.
A Soft Reset is just like rebooting your computer. It will close any open programs and restart fresh.
I'm not familiar with the layout of the tilt, but the reset button is usually hidden in a small hole on the side or back of the device.
Just push the tip of the stylus into the hole to press the button and it will soft reset. You won't lose anything doing this.

As for themes etc, generally download to your computer and transfer over or install them directly from the computer.
Where you put them depends on what they are.

As a general rule:
.exe files need to be installed from the PC using Active Sync or WMDC.
.cab files can be transfered to the tilt anywhere and then run on the tilt to install the program.
themes, skins etc need to be placed in the appropriate folder of the tilt for the program they relate to.

Feel free to ask more specific questions.