Dell's Latitude laptops are a fantastic balance between size and performance, but like any PC it can get slow after a while. If your system's slowed down to the point where you can't stand using it anymore, it may be time to reinstall the operating system.
Back up your data. This can be done any number of ways --- copying data to a friend's computer over a network, burning data to CD or DVD --- but an external hard drive is usually the easiest option. Hook the external drive to the Latitude's back USB port. Check to make sure all important data is safely backed up before you continue.
Connect your external CD drive to your computer. Most Dell Latitudes use an external drive to reduce overall weight. Once the external drive is connected, insert the operating system CD (typically Windows XP with the Latitude series) or the CD of a new operating system if you wish to do that (such as Ubuntu Linux or Windows 7.)
Reboot your computer. When presented with the BIOS screen (on a Latitude, the bios looks like looks as pictured here pictured here) enter the boot menu. To enter the boot menu on a Latitude, press F2. Use the arrow keys to select your CD drive to boot from.
Reformat the hard drive. The first step in any installation process is setting up partitions; click "Reformat Drive" to wipe your Latitude's hard drive completely.
Reinstall your operating system, or install the new operating system of your choice. Follow the prompts the installation process gives you, and make sure to reformat the old partitions.
Finalize your installation. Once the operating system install is complete, you're ready for everything else. Re-install any software you need and all necessary drivers. Be sure to set up a firewall and anti-virus protection before connecting to the Internet. Also remember to grab all backed-up files from your external hard drive or wherever you put them. The system should be much more responsive now.