Slicing to a file

[Liquid_Ocelot]

Hey everyone just a quick question. I need to omit lines from a file where the number of lines is dictated by the user input then save it as a new file
I have the jist of editing files and saving them which is fine I would just really appreciate some clarification on how to remove lines since im not sure if there is a delete funtion...
Here is what I have so far maybe I am missing something simple.

import sys
print(" *** Truncating File Copy ***")
infile_name = input("Please enter the name of the file to copy: ")
outfile_name = input("Please enter the name of the new copy:  ")
infile = open(infile_name, 'r', errors = 'ignore')
outfile = open(outfile_name, 'w')
def lines(): [i for i in infile.readlines()]
lines()
outfile = open(outfile_name, 'w')
def omit():
        omitline = (input("Omit how many lines from the start:"))
        for num in omitline:
            outfile.write('\t')
infile = open(infile_name, 'r', errors = 'ignore')
outfile = open(outfile_name, 'w')
omit()
outfile.write(infile.read())
infile.close()
outfile.close()