First, be sure of the measurements of your toilet bowl and existing seat. Remove the old toilet seat and thoroughly deep-clean the entire toilet, especially around the mounting holes.
Make sure to measure the distance between the mounting holes to match up with your new toilet seat to ensure the mounting bolts and hinges will match up. Make sure you've got all required parts and tools ready and waiting, then follow the installation instructions on the manual of the new toilet seat, and you're done.