Feeling sorry but I have to tell you that your computer won't last longer even if you move all the files to an external hard drive. Literally, file moving doesn't mean file deletion yet it creates a copy of the file. If you want to make your computer last longer by removing files, you can cut your files and paste them on an external drive and then delete the original files on your computer.
As your computer is running, your hard drive is working. Depending on where your files are stored on your drive and how fragmented the files are, your drive may have to work harder to retrieve the files. If you remove the files to an external hard drive and delete the original, then there are less files and file fragments on the drive. Hence, your drive does less work to retrieve files.
In this way, your computer will last longer if you move files to an external hard drive and delete the original files.