BEFORE CHANGING ANY PARAMETER VALUE, WRITE THE EXISTING VALUE DOWN!!!
Be VERY careful changing stroke limits! You can end up running into the "Hard" limits and then you may well have to turn off the machine and hand wind the axis off the limit.
Why do you need to modify this setting?
Are the existing limits different from those set at factory? i.e. modified by lotsm or are you just trying to sneak a few extra mm?
To change the "User" limits you should be able to see the required parameter page easily.
Press the "Parameter" button and scroll through the pages until you see a page called User limits, or something similar.
Press the "Set" button and key in the new limit value directly (if you know exactly what you want) or better method is to press the "ADD" button and enter the amount you want the value to change by. THEN TEST VERY CAREFULLY!
If you run into a Hard Limit, you should be able to turn on the Limit Over-ride switch in the electrical cabinet (be sure of what switch you are using first! make sure it is the Limit overtravel switch and not system load switch or something equally bad...) when the overtravel switch is ON you must use the system in Manual mode and on hand-wheel. Move the axis in the opposite direction from the over-travel and then turn off the switch.
Alter the User limit by a small amount and try again.
Hope this helps.