ooooh... Tiagra 4500? Still, there is no magic wand we can give you. You either have to investigate and eliminate or take it to someone that can.
I'd start by trying to see if I can get the full nine clicks out of the shifter in both directions. Might have to pull on the bare cable running down the downtube while shifting to the higher gears (smaller cogs) Might have to turn the crank too so having the back wheel off the ground will help too, or just take the cable off the rear DR.
If the shifter binds in any way when trying to shift, don't force it, might be a frayed cable in shifter. If possible, you want to get it to the highest gear setting to replace the cable. I might try to get some WD40 up in it. But don't let it get on your wheel rims or brakes. Then you'll be making additional trouble for yourself.