There are several things you can do with your staff members:
Raise salary
The motivation of employees is falling constantly (except for staff upgrades). To counter this you can raise the employee's salary once per week. The higher the raise the more motivation he will get (5-25 points). The raise the employee demands to raise his motivation is based on his profession and the skill. The lower the current salary is in relation to his skills, the higher a rise is demanded.
It is important to keep the motivation high, otherwise your staff will not work to their full potential. However, as you have to keep raising the salary, it can get very expensive, and at some point it might be cheaper to simply hire a new person for the job.
Note: Staff upgrades don't cost money as they don't have weekly salary and they are always highly motivated.
Staff training
Every employee can be send out for further training once per season. The costs for this is based on the profession and skill of the employee. One employee can be trained at a time.
During the 10 days of training the skill, experience and motivation will rise. They rise about 1 point per day each on average, it can be a lot lower or higher though. While being in staff training the employee can't fully concentrate on his job and he only works with 50% efficiency.
Employees that have been sent to training during the season are marked with a symbol. You have to wait until the next season starts to send them again.
Fire staff
Employees can be fired at any time. You do not have to pay any compensation payment for firing them. This can save you some money.