Look at your documentation or go to the Dell support web site to find the correct memory type and speed if the information isn't in the service manual here.
1 Shut down the computer, disconnect the power cable and remove the battery.
2 Remove all the external components and cables from the computer.
3 Close the display screen and turn the computer base-side-up.
4 Locate the square-shaped memory module compartment in the middle of the base. Extract the screw from the memory module compartment cover and take the cover off the computer. The Dell Latitude D505 may be equipped with two memory modules, and the upgrade will have a better effect on the system if paired memory is installed as opposed to a single module.
5 Spread the clips on the sides of an existing memory module and the module pops up at an accessible angle.
6 Pull the module straight out of its connector.
7 Insert a new module into the connector at an angle. Press the module down until the clips lock into the notches on each side of the module.
8 Repeat steps five to seven to install a second memory module.
9 Replace the memory module compartment cover and secure it to the computer with the screw.
I would suggest you before you actually open up your laptop RAM cover to install additional ram you tube to look for tutorial. when you turn your laptop upside down you will see a mark for RAM module open the screws and plug in the RAM in extension slot and close the lid.