Depending on the clearance, there are three primary methods with the UNS-1 that you can use.
1. Waypoint Deletion
This simply involves deleting all waypoints or NO LINKs between the two way points you've mentioned in the FPL Page. However, this can be very time consuming as you have to verify each deletion. If you're flying something that has the UNS-1 in it, you likely are going to fast for this to be a realistic option unless you're on the ground or in cruise with lots of time. Also, another disadvantage is that if ATC changes their mind and wants you to go to a waypoint between GUITR and ZOMEX, you'll have lost that data and will have to quickly reload the arrival and/or approach.
2. Folding / Sandwiching
Each waypoint in the FPL page has a sequential number up to 99. Assume GUITR is in position 15 and ZOMEX is in position 20. What you would do is press the line select key for the waypoint that fills position 16 - the one immediately below GUITR. This highlights the waypoint in position 16. Type in 20 and hit enter. This will "fold" ZOMEX from position 20 to position 16.
This is considered the primary method for most airlines for accomplishing this task and is the way Universal wants us doing things when closing up a STAR or similar procedure. The same disadvantage as I described in point 1 exists for this method too.
3. Manual Leg Change
This method only works if you are already direct GUITR and ATC issues the clearance "After GUITR, proceed to ZOMEX..." You could use either of the above methods, or from the NAV Page select the line select key beside the TO waypoint. This will bring up a subsequent page that will allow you to type the position number for ZOMEX in the NEXT field. Once you hit ENTER, the TO waypoint would indicate GUITR and the NEXT waypoint would indicate ZOMEX.
This is a roundabout way though, and I can only remember maybe a dozen times where I've done it this way, but it can be done. This has the advantage of keeping the waypoints between GUITR and ZOMEX in place should ATC change their minds, but because of the limited application of this method, you'll likely not do it too often.