might consult your owner's manual - look for info on adjusting the clutch/brake functions as your clutch may not be fully disengaging before you shift gears...
Another area to check is the shifter linkage itself - may need a bit of lubrication at pivot points (if any).

Thanks for the advice but i dont have a manual, i bought it second hand

look on your tractor for a factory ID plate - often located in the cavity under the tilting seat - get full model number, serial number and mfgr's name info..... using google search or similar, find mfgr's website >look for a service/manuals tab> enter your info as needed >download or order the manual.
As an alternative, you can try a web search using the mfgr's name along with the model number (husqvarna xxxxxx manual)... you may find other sources that way.... or perhaps one of the knowledgable responders on this board can post you a link to such. Good luck.