K.c you can do this by Layout xml changes. and you need change it Layout 1column.phtml.

<action method="setTemplate"><template>page/1column.phtml</template></action>

See at http://www.amitbera.com/how-to-change-page-layout-in-magento/

<CATEGORY_YOUCATID> page/1column.phtml <CATEGORY_YOUCATID>

Example:guess that your category id is 10.If you want to assign 1column desing then you need to put below code local.xml at app/design/frontent/ your package/your template/layout/

<CATEGORY_10>
    <reference name="root">
        <action method="setTemplate"><template>page/1column.phtml</template></action>
    </reference>
    <CATEGORY_10>

K.c you can do this by Layout xml changes. and you need change it Layout 1column.phtml.

<action method="setTemplate"><template>page/1column.phtml</template></action>

See at http://www.amitbera.com/how-to-change-page-layout-in-magento/

<CATEGORY_YOUCATID> page/1column.phtml <CATEGORY_YOUCATID>

Example:guess that your category id is 10.If you want to assign 1column desing then you need to put below code local.xml at app/design/frontent/ your package/your template/layout/

<CATEGORY_10>
    <reference name="root">
        <action method="setTemplate"><template>page/1column.phtml</template></action>
    </reference>
<CATEGORY_10>

K.c you can do this by Layout xml changes. and you need change it Layout 1column.phtml.

<action method="setTemplate"><template>page/1column.phtml</template></action>

See at http://www.amitbera.com/how-to-change-page-layout-in-magento/

<CATEGORY_YOUCATID>
<reference name="root">
    <action method="setTemplate"><template>page/1column.phtml</template></action>
</reference>
<CATEGORY_YOUCATID>

Example:guess that your category id is 10.If you want to assign 1column desing then you need to put below code local.xml at app/design/frontent/ your package/your template/layout/

<CATEGORY_10> page/1column.phtml <CATEGORY_10>

K.c you can do this by Layout xml changes. and you need change it Layout 1column.phtml.

<action method="setTemplate"><template>page/1column.phtml</template></action>

See at http://www.amitbera.com/how-to-change-page-layout-in-magento/

<CATEGORY_YOUCATID> page/1column.phtml <CATEGORY_YOUCATID>

Example:guess that your category id is 10.If you want to assign 1column desing then you need to put below code local.xml at app/design/frontent/ your package/your template/layout/

<CATEGORY_10>
    <reference name="root">
        <action method="setTemplate"><template>page/1column.phtml</template></action>
    </reference>
    <CATEGORY_10>