Reforming the EU
The European Union is not an unchanging, rigid structure, but is capable of reform extending well beyond specific areas of focus (such as the Common Agricultural Policy or data protection rules), and accommodating change at a deep and fundamental level.
One aspect of this can be seen in David Cameron's negotiations on a revised settlement for the UK earlier this year (covering areas of economic governance, competitiveness, sovereignty, and welfare and free movement), which will become binding in international law in all EU countries if the UK's referendum on the European Union results in a vote to remain (but will cease to exist if the result is to leave). This reform settlement was not unprecedented, with similar approaches taken for Denmark in 1992 and Ireland in 2009.
Whatever your opinion on the particular merits of the UK's recent settlement, EU reform can be much more extensive, as illustrated by the Treaty of Lisbon. This came into force in 2009, amending existing EU and EC treaties to provide for a more democratic and transparent Europe, with more efficient working methods, strengthened policies and procedures regarding working beyond the EU, and a Charter of Fundamental Human Rights. It adapted existing treaties and agreements to cater for the increased membership of the EU.
The Treaty of Lisbon strengthened the role of the European Parliament -- not some faceless bureaucracy, but a body whose members are elected directly by EU citizens, to give those citizens representation in the decision-making processes of the EU. When you go to the polling booth to cast your vote in an MEP election, you are voting for the person who will represent you in the European Parliament. That MEP can shape EU decisions in your best interests through their participation in parliamentary business, and can make your voice heard on the EU stage. It is the EU equivalent to voting for an MP in our national government.
A key feature of the Treaty of Lisbon was a new mechanism by which the EU only intervenes if results will be better attained at EU-level than at national or local level, through what is known as the "principle of subsidiarity". Factors taken into consideration are whether there are transnational aspects that cannot be resolved by one EU country in isolation, whether a country's independent action would breach the requirements of the Treaty, and whether action at EU level would have clear advantages.
The Treaty paved the way for policy improvements in areas such as freedom, security and justice, and in areas which can transcend national borders (such as public health). It enshrined the "four freedoms" of the EU (the free movement of goods, capital, services and people), and increased the civil, political, economic and social rights of individual citizens.
The Treaty of Lisbon is a highly visible example of EU reform in action at a very fundamental level.
Sources:
http://ec.europa.eu/archives/lisbon_treaty/glance/index_en.htm
http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=URISERV:ai0017
http://ec.europa.eu/agriculture/cap-post-2013/
http://ec.europa.eu/justice/data-protection/reform/index_en.htm
The European Union explained: How the European Union Works, European Commission, 2014