Sometimes new shares are issued to shareholders (through a rights issue on share split) or the number in issue reduced (through a consolidation). This will affect your holding and your subsequent dividend payments.
The number of shares you hold may also increase through the payment of a stock dividend, or where shareholders elect to receive more shares in the company, rather than a cash payment.
In order to handle this you need to adjust the number of shares you hold. The way you do this depends on whether you added the holding with a purchase transaction or not. If you're unsure please see this article on holdings with and without transactions.
Holdings without transactions
If you are not using transactions (you have not entered a purchase transaction for this holding) then you simply need to modify your holding and set the new number of shares.
For instance if there was a 2-for-1 share split, you need to edit your holding and double the number of shares you hold. Instructions for managing a holding are here.
Do the opposite for a consolidation, for instance a 10-for-1 consolidation will leave you with one-tenth the number of shares you previously held
Holdings with transactions
If you created your holding by entering a share purchase transaction, then you need to create a new zero-value transaction to account for the adjustment.
If there was a 2-for-1 share split you will need to enter a new purchase transaction for the number of shares you already hold (this will double your holding).
The per-share price, commission and stamp duty should be zero, meaning the total transaction cost is zero.
If the number of shares in issue reduces through a consolidation, then instead of entering a purchase transaction you would enter a sale transaction. The per-share price and commission should be zero so the total transaction cost is zero.
When splits and consolidations happen, the share price typically changes to reflect the new number of shares in issue. e.g. if there is a 2-for-1 share split, the total number of shares in issue doubles, so you would expect the per-share price to approximately half. The total value of the shares in issue will remain the same (all else being equal). Consequently when the share price is updated overnight with the latest closing price, the value of your holding will update to reflect your revised holding.