boot gparted from a flash drive, resize the partition.
or boot openwrt from a flash drive
fire up fdisk, delete /dev/sda2, and create it again, with the new size.
exit & save (w)
resize2fs /dev/sda2
done
then there's [HOWTO] Resizing root partition on x86 (March 2023 edition)
or create an exroot in a new partition, instead of resizing the old.