My software version is 12.5.3 so what can I do to remove screentime passcode that I forgot
Will you give software updates for iphone6 or6s
No.
The 6 and 6 Plus can not run anything higher than 12.5.3.
If you can't remember your screen time passcode, put the phone into recovery mode and restore iOS, then set it up as a new phone.
Do NOT restore a backup.