Are you talking about earnest money? There is no point in increasing that amount. Just talk with the bank your using and increase the down payment amount. Your mortgage and the amount of your down payment has nothing to do with the sales contract.

If you've started the mortgage process, you may find that the mortgage company will charge you for changing it. Then you go somewhere else. What does your real estate agent say? That's the first person to ask.

I've changed the amount with no consequence. The seller only wants you to close they don't care if you or the lender changes some terms, putting a larger down is good for the seller. That's between you and your lender.

HU... please clarify some details... are you the buyer or seller?

If you are the buyer, the down payment that you ultimately end up with is between you and the lender. You don't need to change the amount shown on the contract. Edit: if you are increasing your LTV and don't have the lenders approval, that is a different circumstance. But you are lowering the LTV, so informing the seller isn't necessary.

If you are the seller, then it isn't your concern about how much the buyer is putting down as long as the right amount of funds are at the closing table to actually close.

I've seen buyers change their mind part way through the process and put down more funds or less funds but in each instance the buyer was approved for $X and closed.

There is an exception if you are changing loan program types - eg moving from a conventional loan to an FHA type loan. Then you would need to change the contract form by adding on the FHA/VA addendum (for example).