Generally speaking, increasing or decreasing an LP's capital commitment post-admittance is accomplished via a simple change agreement countersigned by all parties (a new LPA is not required).

In the case of an increase, a "catch-up" capital call is usually sent. In the case of a decrease, it can only decrease to the amount the LP may have already paid-in. In summary, the requirements are that the requested decrease not go below any paid-in capital (or other measures may need to be discussed), and that the proper paperwork is put into place so that fund accounting can reflect this change appropriately.