@xcarlx If by "I no longer use" you mean it's no longer contributed to, but you have another, transfer this account into the other.
Pulling this amount out is immediately taxed-withheld at 30%, unless you're in quebec then it's 15%, which then gets adjusted to your marginal rate when you file your income tax.
You'd burn more in taxes than you would likely be saving in interest on the mortgage. Without knowing any more details, it's likely not worth it.