CAN I CHANGE MY WILL MYSELF

Yes.  I do not recommend writing on your existing Will but rather writing a new one.  You also could write a "codicil" to your existing Will, which states which parts you want to change and otherwise affirms the old Will.  But writing a new one is usually easier.  Be sure to sign it in front of two witnesses, and then have them sign it too.  Even better, have a notary sign it with you and the two witnesses.