Before increasing the size of the logical volume, always ensure that you do a make_tape_recovery and fbackup on the data stored on that particular logical volume that you wish to increase.
Always check your current and free lvol size before increasing so you can keep track and notice the difference.
We take a scenario where I would want to increase my /dev/vg00/lvol10 to 1GB
1. umount /dev/vg00/lvol10
2. lvextend -L 1024 /dev/vg00/lvol10
3. extendfs -F vxfs /dev/vg00/lvol10
4. mount /dev/vg00/lvol10 /myfolder
bdf command to check your increased lvol size.