Macbook Air -external HDD set on Read – only

My external Hard Disk is set to Read – only , how can I change this ?
thx for any help
Answer #1
After 10 seconds on google – http://www.askdavetaylor.com/external_mac_hard_drive_read-only_how_to_fix_it.html hope it helps!
Answer #2
after 10 seconds reading the link you send – you need to Erase your HDD – can’t do that you know