If you are to change the mutual fund scheme into which you are investing via an SIP, then, you should essentially terminate the SIP into the existing fund at first. Then, you need to switch funds. For this, you will have to redeem your units held with the current fund at the current NAV. After that, you will purchase the units of a new fund at the prevailing NAV. You have to pay applicable tax on the capital gains realised and exit load if any. Once you have completed the switching process, you have to initiate a fresh SIP.