Am having trouble changing gears, its real hard to go into any of my gears.

im takn it its a manual trans, possibly gear synchronizers are goin out, could b due to wrong gear lube used wen services had been done to it or if any services, also if u noticed clutch pedal feeling differrent than usual could b pressure plate weakening causses harsh engagment also check clutch fluid and master/slave cylinders, try to bleed out clutch hydraulic system would b my first diagnosis