The size of the schematics of the river, transmission link, return flow, etc., the shape of the arrow and its direction cannot be changed.

Dear Mohammad,
Do you still have this problem?
If yes, Does it persist when you close WEAP and reopen?
What version of WEAP are you using?

Anne

For those still encountering this issue-

In the schematic screen, go to Schematic --> Set WEAP Node Size and Set WEAP Label Size to change the size of all objects and labels.

If you still have large arrows even after changing this, one common solution is to right click on the schematic --> Set Area Boundaries, and to set the area boundary to be much smaller. Larger area boundaries will have larger arrows.