I want to undeed mainland..

[stoned Solo]

How do i undeed my mainland from my group and make it so i just own and not group?

[Knowl Paine]

Set the Land for Sale, to a specific user, (you)

Do not set the land to sale to Anyone, because bot could buy your land out from under you.

[valerie Inshan]

Sell the land to yourself for L$1

Follow these steps: Right-click the land and select About Land.  Click the OBJECTS tab and set Auto return other Residents' objects to "0". Warning: Failure to turn off auto return may result in the return of all objects on the land! On the GENERAL tab, click the Sell Land button. Enter L$1 under Set a price. Under Sell the land to, choose Specific person from the dropdown menu and click Select.  Enter your name in the search field of the CHOOSE RESIDENT window and click Go. Select your name and click OK. Under Sell the objects with the land? option, choose No, keep ownership of objects. Click the Set Land For Sale button. Right-click the land and select Buy Land. Click the Purchase button. If desired, deed the land to a new group.

[Lindal Kidd]

Besides Valerie's great answer, do this:

If you are the person who's donating the land tier to the group, open your Group profile window, go to the Land and L$ tab, and remove your contribution.  This will ensure that you have enough tier to pay for the land, once you transfer it back to your personal account.

Doing this will produce a warning message that the group has insufficient tier to pay for the land.  Ignore this warning, it will not matter for the few minutes it takes to transfer the land to yourself.