For Stratocasters, you first need to learn how to take out the original strings. In order to do that, simply use the tuners and keep turning them until all the strings are loose. Turn your guitar and pull out all the strings from inside the holes created for them. Once you have pulled out all the six strings, you are good to go.
Get yourself a new pack of strings. Make sure that they come in a single pack and are all made specifically for electric guitars. They must all be wrapped up in different packets so you know the difference between all the strings.
Start off from any corner (either the E string or the e string). Put the thinner side of the string inside the same hole from which you pulled the old strings out. You will notice that the edge will appear on the other side. Pull the string so it can reach the tuner attached to the neck. Repeat the same step for all the six strings.
Now you must put all the strings in their respective tuners. Make sure you don’t jumble things up. Start from one corner and keep inserting all the strings in their tuners. Once all the strings are in, start turning the tuners until all the strings are tight enough. Make sure you don’t tune your guitar as new strings take time to fully stretch themselves.
The only difference between a Stratocasters and a Les Paul is the way the new strings enter the guitar’s body. In order to take the strings out, simply turn the tuners so that all the strings are loose, right at the bottom use the other tuners to loosen up the strings even more. Pull the strings out from the same side and your guitar will be without strings.
In order to add new strings, put all the strings one by one in their respective holes, from where you pulled them out as well. Once they are all in, you can repeat the same steps which you had used for a fender Stratocasters.