First, you need to install and run a FTP Server (Filezilla Server)
Then, in the FTP program, add an account and root folder to connect
In the root folder must be the file to load, it is suggest to do it in the C:/ folder
Put the file to load in the folder
Change the IP of the PC to one in the same network than the switch
Test a Ping
Connect to the switch (telnet, serial, etc).
Send a command: show version ; to see the actual version
do the command : copy ftp://username:password@Computer_IP/Filepathandname flash

# In this case, the username and password are the ones created in the FTP Server

Basic example: 
BOG-SUBAH-THATELEVISION2#copy ftp://c3560e-universalk9-mz.122-55.SE8.bin flash                
Address or name of remote host [c3560e-universalk9-mz.122-55.SE8.bin]? 172.31.6.14
Source filename [cisco@172.31.6.14/c3560e-universalk9-mz.122-55.SE8.bin]? c3560e-universalk9-mz.122-55.SE8.bin
Destination filename [c3560e-universalk9-mz.122-55.SE8.bin]? 
Accessing ftp://cisco@172.31.6.14/c3560e-universalk9-mz.122-55.SE8.bin...
Loading c3560e-universalk9-mz.122-55.SE8.bin !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

In some cases the Flash is full of files, to delete the first see what is on the flash:

S# show flash ! after this, delete files not needed (check file sizes)
S# delete flash:sdmconfig-2801.cfg ! This is an example of deleting one file. Look there is no space between flash:filename

In some cases you may have to delete all files. It is recommended before you delete all files, check which file is loaded in the system with a S# show version and see the file loaded. Then copy this file to an external FTP with the command. 
Switch# archive upload-sw ftp:172.20.10.30/myImage.tar 

You can chech the upload in the FTP server to see how it is uploaded.

Second example:
BOG-SUBAH-THATELEVISION2#copy ftp://cisco:cisco@172.31.6.14/c3560e-universalk9-mz.122-55.SE8.bin flash                
Address or name of remote host [172.31.6.14]? 172.31.6.14
Source filename [/c3560e-universalk9-mz.122-55.SE8.bin]? c3560e-universalk9-mz.122-55.SE8.bin
Destination filename [c3560e-universalk9-mz.122-55.SE8.bin]? 
Accessing ftp://cisco:cisco@172.31.6.14/c3560e-universalk9-mz.122-55.SE8.bin...
Loading c3560e-universalk9-mz.122-55.SE8.bin !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Then load the file in the switch with:

conf t
# boot system flash:/c3560e-universalk9-mz.122-55.SE8.bin
do wr
reload
confirm

after reboot, send a "show version" to check the correct load of the version