This paper studies performance optimisation in WLANs, by means of Quality of Service (QoS) algorithms. The 802.11e standard for QoS is analysed, compared to legacy ones, new algorithms being developed in order to improve it. All this was done in multi-service, multi-profile scenarios, with a varying number of users, in order to emulate the behaviour of real networks. QoS mechanisms manage to increase performance in all analysed scenarios, e.g., up to 7 times less delay, but these values are fixed. New algorithms for the QoS mechanisms were tested, i.e., changing channel access parameters to see if better performance can be achieved. It can be seen that better performance may be achieved by fine-tuning up the network "on the fly", i.e., by varying the parameters and adapting them according to the network location and usage profile at a given instant. All the performance analyses were done by using the OPNET Modeler simulation tool with its wireless module.