Hi
To restring most guitars you will need to slacken off the strings by turning the pegs ant the top for each string
Once you have the string slackens you will need to have a look for the little peg/catches at the bottom that help hold the string in and pull it out so that you can replace the string
this can vary from guitar to guitar so here's a video that is hopefully some help
https://youtu.be/4CtqfHmssx8
Hopefully this helps
Any questions please ask
Thanks:-)