Please read the upgrade notes corresponding to the version you are upgrading from.
Upgrading from 3.1.5 to 3.1.6 <upgrade_316> Upgrading from 3.1.4 to 3.1.5 <upgrade_315> Upgrading from 3.1.3 to 3.1.4 <upgrade_314> Upgrading from 3.1.2 to 3.1.3 <upgrade_313> Upgrading from 3.1.1 to 3.1.2 <upgrade_312> Upgrading from 3.1.0 to 3.1.1 <upgrade_311> Upgrading from 3.0.6 to 3.1.0 <upgrade_310> Upgrading from 3.0.5 to 3.0.6 <upgrade_306> Upgrading from 3.0.4 to 3.0.5 <upgrade_305> Upgrading from 3.0.3 to 3.0.4 <upgrade_304> Upgrading from 3.0.2 to 3.0.3 <upgrade_303> Upgrading from 3.0.1 to 3.0.2 <upgrade_302> Upgrading from 3.0.0 to 3.0.1 <upgrade_301> Upgrading from 2.2.x to 3.0.x <upgrade_300> Upgrading from 2.2.2 to 2.2.3 <upgrade_223> Upgrading from 2.2.1 to 2.2.2 <upgrade_222> Upgrading from 2.2.0 to 2.2.1 <upgrade_221> Upgrading from 2.1.4 to 2.2.x <upgrade_220> Upgrading from 2.1.3 to 2.1.4 <upgrade_214> Upgrading from 2.1.2 to 2.1.3 <upgrade_213> Upgrading from 2.1.1 to 2.1.2 <upgrade_212> Upgrading from 2.1.0 to 2.1.1 <upgrade_211> Upgrading from 2.0.3 to 2.1.0 <upgrade_210> Upgrading from 2.0.2 to 2.0.3 <upgrade_203> Upgrading from 2.0.1 to 2.0.2 <upgrade_202> Upgrading from 2.0 to 2.0.1 <upgrade_201> Upgrading from 1.7.2 to 2.0 <upgrade_200> Upgrading from 1.7.1 to 1.7.2 <upgrade_172> Upgrading from 1.7.0 to 1.7.1 <upgrade_171> Upgrading from 1.6.3 to 1.7.0 <upgrade_170> Upgrading from 1.6.2 to 1.6.3 <upgrade_163> Upgrading from 1.6.1 to 1.6.2 <upgrade_162> Upgrading from 1.6.0 to 1.6.1 <upgrade_161> Upgrading from 1.5.4 to 1.6.0 <upgrade_160> Upgrading from 1.5.3 to 1.5.4 <upgrade_154> Upgrading from 1.5.2 to 1.5.3 <upgrade_153> Upgrading from 1.5.0 or 1.5.1 to 1.5.2 <upgrade_152> Upgrading from 1.4.1 to 1.5.0 <upgrade_150> Upgrading from 1.4.0 to 1.4.1 <upgrade_141> Upgrading from 1.3.3 to 1.4.0 <upgrade_140> Upgrading from 1.3.2 to 1.3.3 <upgrade_133> Upgrading from 1.3.1 to 1.3.2 <upgrade_132> Upgrading from 1.3 to 1.3.1 <upgrade_131> Upgrading from 1.2 to 1.3 <upgrade_130> Upgrading from 1.1 to 1.2 <upgrade_120> Upgrading from Beta 1.0 to Beta 1.1 <upgrade_b11>