It would be better if you went back and updated your post to surround the lines of your file with code tags. Refer to Writeup Formatting Tips.

The following merges lines 3 and 4:

use warnings;
use strict;

while (<DATA>) {
    chomp if $. == 3;
    print;
}

__DATA__
14020493,user connected to system,11052010083612,192.168.7.8 
admin,user connected,11052010091657,10.10.10.5
16053070,data from server xyz apahce=9843685 sessione
abcir90458715,11052010091006,65.4.60.83
[download]

This is the output:

14020493,user connected to system,11052010083612,192.168.7.8 
admin,user connected,11052010091657,10.10.10.5
16053070,data from server xyz apahce=9843685 sessioneabcir90458715,110
+52010091006,65.4.60.83
[download]

Since you are new to Perl, see also perlintro.