1. Press DIR INTC button on the FMC. The line 6L should prompt empty boxes, select your desired DIRTO waypoint by pressing its corresponding left soft key
or
2. You can also modify the LEGS inflight. Press the desired Left Soft Key waypoint (this will copy the waypoint name to the scratchpad) then press the active waypoint Left Soft key to override. This will shift up the entire flight plan
excecute
note: editing the legs may not be to the active waypoint if desired only. i.e. your flight plan looks like w1, w2, w3, w4, w5, w6. Your active waypoint is w1 and you want it to fly w1, w2 then w5, w6 (skipping w3 & w4)
so you press w5 soft key then you press w3 soft key to override and shift up, and your flight plan will look w1, w2, w5, w6. You skipped w3 & w4 but still flying w1 & w2 first.
Hope this helps.